Intermediate Geometry : Intermediate Geometry

Study concepts, example questions & explanations for Intermediate Geometry

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Example Questions

Example Question #1 : How To Find The Perimeter Of A Pentagon

If the side of a pentagon is , what is the perimeter?

Possible Answers:

Correct answer:

Explanation:

Write the perimeter formula for pentagons and substitute the side length.

Example Question #2 : How To Find The Perimeter Of A Pentagon

Determine the perimeter of a pentagon if the side length is .

Possible Answers:

Correct answer:

Explanation:

Write the formula to find the perimeter for a pentagon.

Substitute the side into the perimeter formula.

Example Question #5 : How To Find The Perimeter Of A Pentagon

In the figure below, if the length of is one-third the length of , what is the perimeter of the pentagon?

1

Possible Answers:

Correct answer:

Explanation:

1

Notice that the pentagon is made up of one rectangle and two right triangles. Start by finding the lengths of  and .

Let  be the length of . Then, it follows that  is the length of .

From the figure, we know that . Since we are working with a rectangle, .

Now, solve for .

So then, .

Now that we know , we can use the Pythagorean theorem to solve for the length of .

Plug in the lengths of the legs to find the length of the hypotenuse.

Next, find the length of  by using the Pythagorean theorem.

Finally, add up all the side lengths of the pentagon to find its perimeter.

Make sure to round to  places after the decimal.

 

Example Question #6 : How To Find The Perimeter Of A Pentagon

In pentagon  below, the length of  is one-third that of . Find the perimeter of the pentagon.

5

Possible Answers:

Correct answer:

Explanation:

5

Notice that this pentagon is made up of two right triangles and one rectangle.

Start by finding the length of . Since we are given an angle measurement and a length of a leg of the triangle, we can use tangent to find the length of .

Now, we know that  is three times the length of .

Since we have rectangle .

Thus, 

Now, we can use cosine to find the length of .

Next, use the Pythagorean Theorem to find the length of .

Now that we have all the side lengths of the pentagon, we can find its perimeter.

 

Example Question #7 : How To Find The Perimeter Of A Pentagon

In pentagon  below, the length of  is one-third the length of . Find the perimeter of the pentagon.

6

Possible Answers:

Correct answer:

Explanation:

6

Notice that this pentagon is made up of two right triangles and one rectangle.

Start by finding the length of . Since we are given an angle measurement and a length of a leg of the triangle, we can use tangent to find the length of .

Now, we know that  is three times the length of .

Since we have rectangle .

Thus, 

Now, we can use sine to find the length of .

Next, use the Pythagorean Theorem to find the length of .

Now that we have all the side lengths of the pentagon, we can find its perimeter.

Example Question #1 : How To Find The Length Of The Diagonal Of A Pentagon

In the pentagon below, the length of  is one-third that of . Find the length of diagonal .

4

Possible Answers:

Correct answer:

Explanation:

4

Start by using the Pythagorean theorem to find the length of .

Since  is one-third the length of , we know that the length of  must be .

Now, notice that the pentagon is made up of one rectangle and two right triangles.

Focus on rectangle . We can find the length of  by adding together the lengths of  and .

Since we are working with a rectangle, we know that . Thus, we can use the Pythagorean Theorem again to find the length of .

Make sure to round to two places after the decimal.

Example Question #1 : How To Find The Length Of The Diagonal Of A Pentagon

What is the length of a diagonal of a pentagon with side length of 20 centimeters (to the nearest tenth)?

Possible Answers:

Correct answer:

Explanation:

Let  be the length fo a diagonal.

One interior angle of a pentagon measures 

A diagonal of this pentagon, along with two sides, forms an isosceles triangle with sides 20, 20 and ; the side of length   is opposite the angle of measure  , and each side of length 20 is opposite an angle of measure  .

The Law of Sines helps us to determine :

Example Question #753 : Plane Geometry

A regular pentagon has a perimeter of . Find the length of one side of the pentagon. 

Possible Answers:

Correct answer:

Explanation:

By definition a regular pentagon must have five equivalent sides and five equivalent interior angles. Since this problem provides the measurement for the total perimeter of the pentagon, work backwards using the formula: 

, where  the length of one side of the pentagon. 



Example Question #1 : How To Find The Length Of The Side Of A Pentagon

A regular pentagon has a perimeter of . Find the length of one side of the pentagon. 

Possible Answers:

Correct answer:

Explanation:

By definition a regular pentagon must have five equivalent sides and five equivalent interior angles. Since this problem provides the measurement for the total perimeter of the pentagon, work backwards using the formula: 

, where  the length of one side of the pentagon. 



Example Question #1 : How To Find The Length Of The Side Of A Pentagon

A regular pentagon has an area of  square units and an apothem measurement of . Find the length of one side of the pentagon. 

Possible Answers:

Correct answer:

Explanation:

A regular pentagon must have five equivalent sides and five equivalent interior angles. Regular pentagons can be divided up into five equivalent interior triangles, where the base of the triangle is a side length and the height of the triangle is the apothem. This problem provides the total area for the pentagon. 

Therefore, you must work backwards using the area formula: , where the base is equal to the length of one side of the triangle and the height of the triangle is the measurement of the apothem. However, this will only provide the measurement for one of the five interior triangles, thus you first need to divide the total area by 

The solution is:



So, area of one of the five interior triangles is equal to: 

Now, apply the area formula: 





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