Basic Geometry : Triangles

Study concepts, example questions & explanations for Basic Geometry

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Example Questions

Example Question #371 : Triangles

Find the perimeter.

12

Possible Answers:

Correct answer:

Explanation:

How do you find the perimeter of a right triangle?

There are three primary methods used to find the perimeter of a right triangle.

  1. When side lengths are given, add them together.
  2. Solve for a missing side using the Pythagorean theorem.
  3. If we know side-angle-side information, solve for the missing side using the Law of Cosines.

 

Method 1:

This method will show you how to calculate the perimeter of a triangle when all sides lengths are known. Consider the following figure:

Screen shot 2016 07 07 at 11.31.44 am

If we know the lengths of sides , and , then we can simply add them together to find the perimeter of the triangle. It is important to note several things. First, we need to make sure that all the units given match one another. Second, when all the side lengths are known, then the perimeter formula may be used on all types of triangles (e.g. right, acute, obtuse, equilateral, isosceles, and scalene). The perimeter formula is written formally in the following format:

 

Method 2:

In right triangles, we can calculate the perimeter of a triangle when we are provided only two sides. We can do this by using the Pythagorean theorem. Let's first discuss right triangles in a general sense. A right triangle is a triangle that has one  angle. It is a special triangle and needs to be labeled accordingly. The legs of the triangle form the  angle and they are labeled  and . The side of the triangle that is opposite of the  angle and connects the two legs is known as the hypotenuse. The hypotenuse is the longest side of the triangle and is labeled as .

 

Screen shot 2016 07 07 at 10.13.54 am

If a triangle appears in this format, then we can use the Pythagorean theorem to solve for any missing side. This formula is written in the following manner:

We can rearrange it in a number of ways to solve for each of the sides of the triangle. Let's rearrange it to solve for the hypotenuse, .

Rearrange and take the square root of both sides. 

Simplify.

Now, let's use the Pythagorean theorem to solve for one of the legs, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

Last, let's use the Pythagorean theorem to solve for the adjacent leg, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

It is important to note that we can only use the following formulas to solve for the missing side of a right triangle when two other sides are known:

After we find the missing side, we can use the perimeter formula to calculate the triangle's perimeter.  

 

Method 3:

This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. When we know side-angle-side (SAS) information, we can use the Law of Cosines to find the missing side. In order for this formula to accurately calculate the missing side we need to label the triangle in the following manner:

Screen shot 2016 07 07 at 12.58.14 pm

When the triangle is labeled in this way each side directly corresponds to the angle directly opposite of it. If we label our triangle carefully, then we can use the following formulas to find missing sides in any triangle given SAS information:

After, we calculate the right side of the equation, we need to take the square root of both sides in order to obtain the final side length of the missing side. Last, we need to use the perimeter formula to obtain the distance of the side lengths of the polygon.

 

Solution:

Now, that we have discussed the three methods used to calculate the perimeter of a triangle, we can use this information to solve the problem.

13

In order to find the perimeter, we must first find the length of the hypotenuse of the right triangle.

Use Pythagorean's theorem to find the length of the hypotenuse:

Plug in the values of the lengths of the legs of the given triangle.

Now, recall how to find the perimeter of a triangle:

Plug in all the values of the sides of the triangle to find the perimeter.

Make sure to round to  places after the decimal.

Example Question #372 : Triangles

Find the perimeter.

11

Possible Answers:

Correct answer:

Explanation:

How do you find the perimeter of a right triangle?

There are three primary methods used to find the perimeter of a right triangle.

  1. When side lengths are given, add them together.
  2. Solve for a missing side using the Pythagorean theorem.
  3. If we know side-angle-side information, solve for the missing side using the Law of Cosines.

 

Method 1:

This method will show you how to calculate the perimeter of a triangle when all sides lengths are known. Consider the following figure:

Screen shot 2016 07 07 at 11.31.44 am

If we know the lengths of sides , and , then we can simply add them together to find the perimeter of the triangle. It is important to note several things. First, we need to make sure that all the units given match one another. Second, when all the side lengths are known, then the perimeter formula may be used on all types of triangles (e.g. right, acute, obtuse, equilateral, isosceles, and scalene). The perimeter formula is written formally in the following format:

 

Method 2:

In right triangles, we can calculate the perimeter of a triangle when we are provided only two sides. We can do this by using the Pythagorean theorem. Let's first discuss right triangles in a general sense. A right triangle is a triangle that has one  angle. It is a special triangle and needs to be labeled accordingly. The legs of the triangle form the  angle and they are labeled  and . The side of the triangle that is opposite of the  angle and connects the two legs is known as the hypotenuse. The hypotenuse is the longest side of the triangle and is labeled as .

 

Screen shot 2016 07 07 at 10.13.54 am

If a triangle appears in this format, then we can use the Pythagorean theorem to solve for any missing side. This formula is written in the following manner:

We can rearrange it in a number of ways to solve for each of the sides of the triangle. Let's rearrange it to solve for the hypotenuse, .

Rearrange and take the square root of both sides. 

Simplify.

Now, let's use the Pythagorean theorem to solve for one of the legs, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

Last, let's use the Pythagorean theorem to solve for the adjacent leg, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

It is important to note that we can only use the following formulas to solve for the missing side of a right triangle when two other sides are known:

After we find the missing side, we can use the perimeter formula to calculate the triangle's perimeter.  

 

Method 3:

This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. When we know side-angle-side (SAS) information, we can use the Law of Cosines to find the missing side. In order for this formula to accurately calculate the missing side we need to label the triangle in the following manner:

Screen shot 2016 07 07 at 12.58.14 pm

When the triangle is labeled in this way each side directly corresponds to the angle directly opposite of it. If we label our triangle carefully, then we can use the following formulas to find missing sides in any triangle given SAS information:

After, we calculate the right side of the equation, we need to take the square root of both sides in order to obtain the final side length of the missing side. Last, we need to use the perimeter formula to obtain the distance of the side lengths of the polygon.

 

Solution:

Now, that we have discussed the three methods used to calculate the perimeter of a triangle, we can use this information to solve the problem.

13

In order to find the perimeter, we must first find the length of the hypotenuse of the right triangle.

Use Pythagorean's theorem to find the length of the hypotenuse:

Plug in the values of the lengths of the legs of the given triangle.

Now, recall how to find the perimeter of a triangle:

Plug in all the values of the sides of the triangle to find the perimeter.

Make sure to round to  places after the decimal.

Example Question #373 : Triangles

Find the perimeter of a right isosceles triangle with the following side length:

Possible Answers:

Correct answer:

Explanation:

How do you find the perimeter of a right triangle?

There are three primary methods used to find the perimeter of a right triangle.

  1. When side lengths are given, add them together.
  2. Solve for a missing side using the Pythagorean theorem.
  3. If we know side-angle-side information, solve for the missing side using the Law of Cosines.

 

Method 1:

This method will show you how to calculate the perimeter of a triangle when all sides lengths are known. Consider the following figure:

Screen shot 2016 07 07 at 11.31.44 am

If we know the lengths of sides , and , then we can simply add them together to find the perimeter of the triangle. It is important to note several things. First, we need to make sure that all the units given match one another. Second, when all the side lengths are known, then the perimeter formula may be used on all types of triangles (e.g. right, acute, obtuse, equilateral, isosceles, and scalene). The perimeter formula is written formally in the following format:

 

Method 2:

In right triangles, we can calculate the perimeter of a triangle when we are provided only two sides. We can do this by using the Pythagorean theorem. Let's first discuss right triangles in a general sense. A right triangle is a triangle that has one  angle. It is a special triangle and needs to be labeled accordingly. The legs of the triangle form the  angle and they are labeled  and . The side of the triangle that is opposite of the  angle and connects the two legs is known as the hypotenuse. The hypotenuse is the longest side of the triangle and is labeled as .

 

Screen shot 2016 07 07 at 10.13.54 am

If a triangle appears in this format, then we can use the Pythagorean theorem to solve for any missing side. This formula is written in the following manner:

We can rearrange it in a number of ways to solve for each of the sides of the triangle. Let's rearrange it to solve for the hypotenuse, .

Rearrange and take the square root of both sides. 

Simplify.

Now, let's use the Pythagorean theorem to solve for one of the legs, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

Last, let's use the Pythagorean theorem to solve for the adjacent leg, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

It is important to note that we can only use the following formulas to solve for the missing side of a right triangle when two other sides are known:

After we find the missing side, we can use the perimeter formula to calculate the triangle's perimeter.  

 

Method 3:

This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. When we know side-angle-side (SAS) information, we can use the Law of Cosines to find the missing side. In order for this formula to accurately calculate the missing side we need to label the triangle in the following manner:

Screen shot 2016 07 07 at 12.58.14 pm

When the triangle is labeled in this way each side directly corresponds to the angle directly opposite of it. If we label our triangle carefully, then we can use the following formulas to find missing sides in any triangle given SAS information:

After, we calculate the right side of the equation, we need to take the square root of both sides in order to obtain the final side length of the missing side. Last, we need to use the perimeter formula to obtain the distance of the side lengths of the polygon.

 

Solution:

Now, that we have discussed the three methods used to calculate the perimeter of a triangle, we can use this information to solve the problem.

Recall how to find the perimeter of a triangle:

The given triangle has  of the three sides needed. Use the Pythagorean theorem to find the length of the third side.

Recall the Pythagorean theorem:

In this case, perimeter is side+side+hypotenuse. The two sides are 6cm, we need to find the hypotenuse using Pythagorean theorem.

Example Question #374 : Triangles

Find the perimeter, , of a right triangle whose sides are A,B, and hypotenuse C.

Given, 

Possible Answers:

Correct answer:

Explanation:

How do you find the perimeter of a right triangle?

There are three primary methods used to find the perimeter of a right triangle.

  1. When side lengths are given, add them together.
  2. Solve for a missing side using the Pythagorean theorem.
  3. If we know side-angle-side information, solve for the missing side using the Law of Cosines.

 

Method 1:

This method will show you how to calculate the perimeter of a triangle when all sides lengths are known. Consider the following figure:

Screen shot 2016 07 07 at 11.31.44 am

If we know the lengths of sides , and , then we can simply add them together to find the perimeter of the triangle. It is important to note several things. First, we need to make sure that all the units given match one another. Second, when all the side lengths are known, then the perimeter formula may be used on all types of triangles (e.g. right, acute, obtuse, equilateral, isosceles, and scalene). The perimeter formula is written formally in the following format:

 

Method 2:

In right triangles, we can calculate the perimeter of a triangle when we are provided only two sides. We can do this by using the Pythagorean theorem. Let's first discuss right triangles in a general sense. A right triangle is a triangle that has one  angle. It is a special triangle and needs to be labeled accordingly. The legs of the triangle form the  angle and they are labeled  and . The side of the triangle that is opposite of the  angle and connects the two legs is known as the hypotenuse. The hypotenuse is the longest side of the triangle and is labeled as .

 

Screen shot 2016 07 07 at 10.13.54 am

If a triangle appears in this format, then we can use the Pythagorean theorem to solve for any missing side. This formula is written in the following manner:

We can rearrange it in a number of ways to solve for each of the sides of the triangle. Let's rearrange it to solve for the hypotenuse, .

Rearrange and take the square root of both sides. 

Simplify.

Now, let's use the Pythagorean theorem to solve for one of the legs, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

Last, let's use the Pythagorean theorem to solve for the adjacent leg, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

It is important to note that we can only use the following formulas to solve for the missing side of a right triangle when two other sides are known:

After we find the missing side, we can use the perimeter formula to calculate the triangle's perimeter.  

 

Method 3:

This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. When we know side-angle-side (SAS) information, we can use the Law of Cosines to find the missing side. In order for this formula to accurately calculate the missing side we need to label the triangle in the following manner:

Screen shot 2016 07 07 at 12.58.14 pm

When the triangle is labeled in this way each side directly corresponds to the angle directly opposite of it. If we label our triangle carefully, then we can use the following formulas to find missing sides in any triangle given SAS information:

After, we calculate the right side of the equation, we need to take the square root of both sides in order to obtain the final side length of the missing side. Last, we need to use the perimeter formula to obtain the distance of the side lengths of the polygon.

 

Solution:

Now, that we have discussed the three methods used to calculate the perimeter of a triangle, we can use this information to solve the problem.

Recall how to find the perimeter of a triangle:

The given triangle has  of the three sides needed. Use the Pythagorean theorem to find the length of the third side.

Recall the Pythagorean theorem:

Rearrange to solve for the hypotenuse.

We then add up all of the sides. 

Example Question #181 : Right Triangles

Which of the following could NOT be the perimeter of a right triangle with sides of length  and

Possible Answers:

All of these work 

None of these work

Correct answer:

Explanation:

How do you find the perimeter of a right triangle?

There are three primary methods used to find the perimeter of a right triangle.

  1. When side lengths are given, add them together.
  2. Solve for a missing side using the Pythagorean theorem.
  3. If we know side-angle-side information, solve for the missing side using the Law of Cosines.

 

Method 1:

This method will show you how to calculate the perimeter of a triangle when all sides lengths are known. Consider the following figure:

Screen shot 2016 07 07 at 11.31.44 am

If we know the lengths of sides , and , then we can simply add them together to find the perimeter of the triangle. It is important to note several things. First, we need to make sure that all the units given match one another. Second, when all the side lengths are known, then the perimeter formula may be used on all types of triangles (e.g. right, acute, obtuse, equilateral, isosceles, and scalene). The perimeter formula is written formally in the following format:

 

Method 2:

In right triangles, we can calculate the perimeter of a triangle when we are provided only two sides. We can do this by using the Pythagorean theorem. Let's first discuss right triangles in a general sense. A right triangle is a triangle that has one  angle. It is a special triangle and needs to be labeled accordingly. The legs of the triangle form the  angle and they are labeled  and . The side of the triangle that is opposite of the  angle and connects the two legs is known as the hypotenuse. The hypotenuse is the longest side of the triangle and is labeled as .

 

Screen shot 2016 07 07 at 10.13.54 am

If a triangle appears in this format, then we can use the Pythagorean theorem to solve for any missing side. This formula is written in the following manner:

We can rearrange it in a number of ways to solve for each of the sides of the triangle. Let's rearrange it to solve for the hypotenuse, .

Rearrange and take the square root of both sides. 

Simplify.

Now, let's use the Pythagorean theorem to solve for one of the legs, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

Last, let's use the Pythagorean theorem to solve for the adjacent leg, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

It is important to note that we can only use the following formulas to solve for the missing side of a right triangle when two other sides are known:

After we find the missing side, we can use the perimeter formula to calculate the triangle's perimeter.  

 

Method 3:

This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. When we know side-angle-side (SAS) information, we can use the Law of Cosines to find the missing side. In order for this formula to accurately calculate the missing side we need to label the triangle in the following manner:

Screen shot 2016 07 07 at 12.58.14 pm

When the triangle is labeled in this way each side directly corresponds to the angle directly opposite of it. If we label our triangle carefully, then we can use the following formulas to find missing sides in any triangle given SAS information:

After, we calculate the right side of the equation, we need to take the square root of both sides in order to obtain the final side length of the missing side. Last, we need to use the perimeter formula to obtain the distance of the side lengths of the polygon.

 

Solution:

Now, that we have discussed the three methods used to calculate the perimeter of a triangle, we can use this information to solve the problem.

Since it wasn't specified if the two lengths given were the legs, or a leg and the hypotenuse, there are 2 options for the third side length. 

Option 1: 

To find the perimeter, add the following:

Option 2: 

To find the perimeter, add the following:

The only option listed that isn't either of those is , so that is the answer. 

Example Question #31 : How To Find The Perimeter Of A Right Triangle

Which of these could NOT be the perimeter of a right triangle with sides of length  and

Possible Answers:

None of these work. 

All of these work

Correct answer:

Explanation:

How do you find the perimeter of a right triangle?

There are three primary methods used to find the perimeter of a right triangle.

  1. When side lengths are given, add them together.
  2. Solve for a missing side using the Pythagorean theorem.
  3. If we know side-angle-side information, solve for the missing side using the Law of Cosines.

 

Method 1:

This method will show you how to calculate the perimeter of a triangle when all sides lengths are known. Consider the following figure:

Screen shot 2016 07 07 at 11.31.44 am

If we know the lengths of sides , and , then we can simply add them together to find the perimeter of the triangle. It is important to note several things. First, we need to make sure that all the units given match one another. Second, when all the side lengths are known, then the perimeter formula may be used on all types of triangles (e.g. right, acute, obtuse, equilateral, isosceles, and scalene). The perimeter formula is written formally in the following format:

 

Method 2:

In right triangles, we can calculate the perimeter of a triangle when we are provided only two sides. We can do this by using the Pythagorean theorem. Let's first discuss right triangles in a general sense. A right triangle is a triangle that has one  angle. It is a special triangle and needs to be labeled accordingly. The legs of the triangle form the  angle and they are labeled  and . The side of the triangle that is opposite of the  angle and connects the two legs is known as the hypotenuse. The hypotenuse is the longest side of the triangle and is labeled as .

 

Screen shot 2016 07 07 at 10.13.54 am

If a triangle appears in this format, then we can use the Pythagorean theorem to solve for any missing side. This formula is written in the following manner:

We can rearrange it in a number of ways to solve for each of the sides of the triangle. Let's rearrange it to solve for the hypotenuse, .

Rearrange and take the square root of both sides. 

Simplify.

Now, let's use the Pythagorean theorem to solve for one of the legs, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

Last, let's use the Pythagorean theorem to solve for the adjacent leg, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

It is important to note that we can only use the following formulas to solve for the missing side of a right triangle when two other sides are known:

After we find the missing side, we can use the perimeter formula to calculate the triangle's perimeter.  

 

Method 3:

This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. When we know side-angle-side (SAS) information, we can use the Law of Cosines to find the missing side. In order for this formula to accurately calculate the missing side we need to label the triangle in the following manner:

Screen shot 2016 07 07 at 12.58.14 pm

When the triangle is labeled in this way each side directly corresponds to the angle directly opposite of it. If we label our triangle carefully, then we can use the following formulas to find missing sides in any triangle given SAS information:

After, we calculate the right side of the equation, we need to take the square root of both sides in order to obtain the final side length of the missing side. Last, we need to use the perimeter formula to obtain the distance of the side lengths of the polygon.

 

Solution:

Now, that we have discussed the three methods used to calculate the perimeter of a triangle, we can use this information to solve the problem.

Since it wasn't specified if the two lengths given were the legs, or a leg and the hypotenuse, there are 2 options for the third side length. 

Option 1: 

To find the perimeter, add the following:

Option 2: 

To find the perimeter, add the following:

The only option listed that isn't either of those is , so that is the answer. 

Example Question #183 : Right Triangles

Shape area right triangle

In the right triangle shown here, the length of the hypotenuse  is  units and the length of its base  is  units. What is its perimeter in units?

Possible Answers:

Correct answer:

Explanation:

How do you find the perimeter of a right triangle?

There are three primary methods used to find the perimeter of a right triangle.

  1. When side lengths are given, add them together.
  2. Solve for a missing side using the Pythagorean theorem.
  3. If we know side-angle-side information, solve for the missing side using the Law of Cosines.

 

Method 1:

This method will show you how to calculate the perimeter of a triangle when all sides lengths are known. Consider the following figure:

Screen shot 2016 07 07 at 11.31.44 am

If we know the lengths of sides , and , then we can simply add them together to find the perimeter of the triangle. It is important to note several things. First, we need to make sure that all the units given match one another. Second, when all the side lengths are known, then the perimeter formula may be used on all types of triangles (e.g. right, acute, obtuse, equilateral, isosceles, and scalene). The perimeter formula is written formally in the following format:

 

Method 2:

In right triangles, we can calculate the perimeter of a triangle when we are provided only two sides. We can do this by using the Pythagorean theorem. Let's first discuss right triangles in a general sense. A right triangle is a triangle that has one  angle. It is a special triangle and needs to be labeled accordingly. The legs of the triangle form the  angle and they are labeled  and . The side of the triangle that is opposite of the  angle and connects the two legs is known as the hypotenuse. The hypotenuse is the longest side of the triangle and is labeled as .

 

Screen shot 2016 07 07 at 10.13.54 am

If a triangle appears in this format, then we can use the Pythagorean theorem to solve for any missing side. This formula is written in the following manner:

We can rearrange it in a number of ways to solve for each of the sides of the triangle. Let's rearrange it to solve for the hypotenuse, .

Rearrange and take the square root of both sides. 

Simplify.

Now, let's use the Pythagorean theorem to solve for one of the legs, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

Last, let's use the Pythagorean theorem to solve for the adjacent leg, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

It is important to note that we can only use the following formulas to solve for the missing side of a right triangle when two other sides are known:

After we find the missing side, we can use the perimeter formula to calculate the triangle's perimeter.  

 

Method 3:

This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. When we know side-angle-side (SAS) information, we can use the Law of Cosines to find the missing side. In order for this formula to accurately calculate the missing side we need to label the triangle in the following manner:

Screen shot 2016 07 07 at 12.58.14 pm

When the triangle is labeled in this way each side directly corresponds to the angle directly opposite of it. If we label our triangle carefully, then we can use the following formulas to find missing sides in any triangle given SAS information:

After, we calculate the right side of the equation, we need to take the square root of both sides in order to obtain the final side length of the missing side. Last, we need to use the perimeter formula to obtain the distance of the side lengths of the polygon.

 

Solution:

Now, that we have discussed the three methods used to calculate the perimeter of a triangle, we can use this information to solve the problem.

First, we can calculate the height  of this triangle by the Pythagorean theorem:

.

Second, we can add together the lengths of the three sides of this triangle to yield its perimeter. In this case, the perimeter of the triangle is  units.

Example Question #184 : Right Triangles

Right triangle

True or false: The provided triangle has the following perimeter:

Possible Answers:

True

False

Correct answer:

True

Explanation:

How do you find the perimeter of a right triangle?

There are three primary methods used to find the perimeter of a right triangle.

  1. When side lengths are given, add them together.
  2. Solve for a missing side using the Pythagorean theorem.
  3. If we know side-angle-side information, solve for the missing side using the Law of Cosines.

 

Method 1:

This method will show you how to calculate the perimeter of a triangle when all sides lengths are known. Consider the following figure:

Screen shot 2016 07 07 at 11.31.44 am

If we know the lengths of sides , and , then we can simply add them together to find the perimeter of the triangle. It is important to note several things. First, we need to make sure that all the units given match one another. Second, when all the side lengths are known, then the perimeter formula may be used on all types of triangles (e.g. right, acute, obtuse, equilateral, isosceles, and scalene). The perimeter formula is written formally in the following format:

 

Method 2:

In right triangles, we can calculate the perimeter of a triangle when we are provided only two sides. We can do this by using the Pythagorean theorem. Let's first discuss right triangles in a general sense. A right triangle is a triangle that has one  angle. It is a special triangle and needs to be labeled accordingly. The legs of the triangle form the  angle and they are labeled  and . The side of the triangle that is opposite of the  angle and connects the two legs is known as the hypotenuse. The hypotenuse is the longest side of the triangle and is labeled as .

 

Screen shot 2016 07 07 at 10.13.54 am

If a triangle appears in this format, then we can use the Pythagorean theorem to solve for any missing side. This formula is written in the following manner:

We can rearrange it in a number of ways to solve for each of the sides of the triangle. Let's rearrange it to solve for the hypotenuse, .

Rearrange and take the square root of both sides. 

Simplify.

Now, let's use the Pythagorean theorem to solve for one of the legs, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

Last, let's use the Pythagorean theorem to solve for the adjacent leg, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

It is important to note that we can only use the following formulas to solve for the missing side of a right triangle when two other sides are known:

After we find the missing side, we can use the perimeter formula to calculate the triangle's perimeter.  

 

Method 3:

This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. When we know side-angle-side (SAS) information, we can use the Law of Cosines to find the missing side. In order for this formula to accurately calculate the missing side we need to label the triangle in the following manner:

Screen shot 2016 07 07 at 12.58.14 pm

When the triangle is labeled in this way each side directly corresponds to the angle directly opposite of it. If we label our triangle carefully, then we can use the following formulas to find missing sides in any triangle given SAS information:

After, we calculate the right side of the equation, we need to take the square root of both sides in order to obtain the final side length of the missing side. Last, we need to use the perimeter formula to obtain the distance of the side lengths of the polygon.

 

Solution:

Now, that we have discussed the three methods used to calculate the perimeter of a triangle, we can use this information to solve the problem.

The perimeter of a polygon is the sum of the lengths of its sides. We know the lengths of two sides of the triangle - the lengths of its legs, 9 and 12. We can find the length of the hypotenuse by way of the Pythagorean theorem:

Set , and solve for :

The perimeter is the sum of the lengths of the sides:

.

Example Question #1361 : Basic Geometry

Righttriangle

Given:

What is the perimeter of the right triangle? 

Possible Answers:

None of these

Correct answer:

Explanation:

How do you find the perimeter of a right triangle?

There are three primary methods used to find the perimeter of a right triangle.

  1. When side lengths are given, add them together.
  2. Solve for a missing side using the Pythagorean theorem.
  3. If we know side-angle-side information, solve for the missing side using the Law of Cosines.

 

Method 1:

This method will show you how to calculate the perimeter of a triangle when all sides lengths are known. Consider the following figure:

Screen shot 2016 07 07 at 11.31.44 am

If we know the lengths of sides , and , then we can simply add them together to find the perimeter of the triangle. It is important to note several things. First, we need to make sure that all the units given match one another. Second, when all the side lengths are known, then the perimeter formula may be used on all types of triangles (e.g. right, acute, obtuse, equilateral, isosceles, and scalene). The perimeter formula is written formally in the following format:

 

Method 2:

In right triangles, we can calculate the perimeter of a triangle when we are provided only two sides. We can do this by using the Pythagorean theorem. Let's first discuss right triangles in a general sense. A right triangle is a triangle that has one  angle. It is a special triangle and needs to be labeled accordingly. The legs of the triangle form the  angle and they are labeled  and . The side of the triangle that is opposite of the  angle and connects the two legs is known as the hypotenuse. The hypotenuse is the longest side of the triangle and is labeled as .

 

Screen shot 2016 07 07 at 10.13.54 am

If a triangle appears in this format, then we can use the Pythagorean theorem to solve for any missing side. This formula is written in the following manner:

We can rearrange it in a number of ways to solve for each of the sides of the triangle. Let's rearrange it to solve for the hypotenuse, .

Rearrange and take the square root of both sides. 

Simplify.

Now, let's use the Pythagorean theorem to solve for one of the legs, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

Last, let's use the Pythagorean theorem to solve for the adjacent leg, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

It is important to note that we can only use the following formulas to solve for the missing side of a right triangle when two other sides are known:

After we find the missing side, we can use the perimeter formula to calculate the triangle's perimeter.  

 

Method 3:

This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. When we know side-angle-side (SAS) information, we can use the Law of Cosines to find the missing side. In order for this formula to accurately calculate the missing side we need to label the triangle in the following manner:

Screen shot 2016 07 07 at 12.58.14 pm

When the triangle is labeled in this way each side directly corresponds to the angle directly opposite of it. If we label our triangle carefully, then we can use the following formulas to find missing sides in any triangle given SAS information:

After, we calculate the right side of the equation, we need to take the square root of both sides in order to obtain the final side length of the missing side. Last, we need to use the perimeter formula to obtain the distance of the side lengths of the polygon.

 

Solution:

Now, that we have discussed the three methods used to calculate the perimeter of a triangle, we can use this information to solve the problem.

First, we must determine the length of side B. To do this, we use the Pythagorean theorem, which shows that:

Through substitution, we know that:

Once we know the length of side B, we can find the perimeter by adding the lengths of each side:

Since the problem is given with the unit "inches" we know that the answer is ; converting this to feet gives us the correct answer:

 

Example Question #1362 : Basic Geometry

Find the perimeter of this right triangle.

Triangle_9_b_11

Possible Answers:

None of these

Correct answer:

Explanation:

How do you find the perimeter of a right triangle?

There are three primary methods used to find the perimeter of a right triangle.

  1. When side lengths are given, add them together.
  2. Solve for a missing side using the Pythagorean theorem.
  3. If we know side-angle-side information, solve for the missing side using the Law of Cosines.

 

Method 1:

This method will show you how to calculate the perimeter of a triangle when all sides lengths are known. Consider the following figure:

Screen shot 2016 07 07 at 11.31.44 am

If we know the lengths of sides , and , then we can simply add them together to find the perimeter of the triangle. It is important to note several things. First, we need to make sure that all the units given match one another. Second, when all the side lengths are known, then the perimeter formula may be used on all types of triangles (e.g. right, acute, obtuse, equilateral, isosceles, and scalene). The perimeter formula is written formally in the following format:

 

Method 2:

In right triangles, we can calculate the perimeter of a triangle when we are provided only two sides. We can do this by using the Pythagorean theorem. Let's first discuss right triangles in a general sense. A right triangle is a triangle that has one  angle. It is a special triangle and needs to be labeled accordingly. The legs of the triangle form the  angle and they are labeled  and . The side of the triangle that is opposite of the  angle and connects the two legs is known as the hypotenuse. The hypotenuse is the longest side of the triangle and is labeled as .

 

Screen shot 2016 07 07 at 10.13.54 am

If a triangle appears in this format, then we can use the Pythagorean theorem to solve for any missing side. This formula is written in the following manner:

We can rearrange it in a number of ways to solve for each of the sides of the triangle. Let's rearrange it to solve for the hypotenuse, .

Rearrange and take the square root of both sides. 

Simplify.

Now, let's use the Pythagorean theorem to solve for one of the legs, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

Last, let's use the Pythagorean theorem to solve for the adjacent leg, .

Subtract  from both sides of the equation.

Take the square root of both sides.

Simplify.

It is important to note that we can only use the following formulas to solve for the missing side of a right triangle when two other sides are known:

After we find the missing side, we can use the perimeter formula to calculate the triangle's perimeter.  

 

Method 3:

This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. When we know side-angle-side (SAS) information, we can use the Law of Cosines to find the missing side. In order for this formula to accurately calculate the missing side we need to label the triangle in the following manner:

Screen shot 2016 07 07 at 12.58.14 pm

When the triangle is labeled in this way each side directly corresponds to the angle directly opposite of it. If we label our triangle carefully, then we can use the following formulas to find missing sides in any triangle given SAS information:

After, we calculate the right side of the equation, we need to take the square root of both sides in order to obtain the final side length of the missing side. Last, we need to use the perimeter formula to obtain the distance of the side lengths of the polygon.

 

Solution:

Now, that we have discussed the three methods used to calculate the perimeter of a triangle, we can use this information to solve the problem.

Before we can find the perimeter of this triangle, we need to find the length of side 'b'. Use the Pythagorean theorem and substitute.

Knowing that c=11 and a=9, we can find b.

Now that we know what b is, we can find the perimeter using this formula:

Basically, it is just adding the length of all sides.

 

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