High School Math : How to find the perimeter of a right triangle

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #82 : Right Triangles

What is the perimeter of a triangle with side lengths of 5, 12, and 13?

Possible Answers:

\(\displaystyle 29\)

\(\displaystyle 30\)

\(\displaystyle 32\)

\(\displaystyle 31\)

Correct answer:

\(\displaystyle 30\)

Explanation:

To find the perimeter of a triangle you must add all of the side lengths together. 

In this case our equation would look like \(\displaystyle 5+12+13\)

Add the numbers together to get the answer \(\displaystyle 30\).

Example Question #11 : Triangles

Three points in the xy-coordinate system form a triangle.

The points are \(\displaystyle (-1,5) (-1,1) (4,5)\).

What is the perimeter of the triangle?

Possible Answers:

9 + \sqrt{26}\(\displaystyle 9 + \sqrt{26}\)

\(\displaystyle 9\)

9 + \sqrt{41}\(\displaystyle 9 + \sqrt{41}\)

9 + \sqrt{71}\(\displaystyle 9 + \sqrt{71}\)

Correct answer:

9 + \sqrt{41}\(\displaystyle 9 + \sqrt{41}\)

Explanation:

Drawing points gives sides of a right triangle of 4, 5, and an unknown hypotenuse.

Using the pythagorean theorem we find that the hypotenuse is \sqrt{41}\(\displaystyle \sqrt{41}\).

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

Find the perimeter of the following triangle:

Screen_shot_2014-03-01_at_9.07.42_pm

Possible Answers:

\(\displaystyle 6+6\sqrt{3}m\)

\(\displaystyle 6+2\sqrt{3}m\)

\(\displaystyle 6\sqrt{3}m\)

\(\displaystyle 2\sqrt{3}m\)

\(\displaystyle 2+2\sqrt{3}m\)

Correct answer:

\(\displaystyle 6+2\sqrt{3}m\)

Explanation:

The formula for the perimeter of a right triangle is:

\(\displaystyle P = s_1 + s_2 + s_3\)

where \(\displaystyle s\) is the length of a side.

 

Use the formulas for a a \(\displaystyle 30-60-90\) triangle to find the length of the base. The formula for a \(\displaystyle 30-60-90\) triangle is \(\displaystyle a-a \sqrt{3}-2a\).

Our \(\displaystyle 30-60-90\) triangle is: \(\displaystyle 2m-2\sqrt{3}m-4m\)

 

Plugging in our values, we get:

\(\displaystyle P = 2m+4m+2\sqrt{3}m = 6m+2\sqrt{3}m\)

Example Question #3 : How To Find The Perimeter Of A Right Triangle

Find the perimeter of the following right triangle:

Screen_shot_2014-03-01_at_9.09.16_pm

Possible Answers:

\(\displaystyle 16\sqrt{2}+8m\)

\(\displaystyle 8\sqrt{2}m\)

\(\displaystyle 8\sqrt{2}+8m\)

\(\displaystyle 16\sqrt{2}m\)

\(\displaystyle 16m\)

Correct answer:

\(\displaystyle 8\sqrt{2}+8m\)

Explanation:

The formula for the perimeter of a right triangle is:

\(\displaystyle P = s_1 + s_2 + s_3\)

where \(\displaystyle s\) is the length of a side.

 

Use the formulas for a \(\displaystyle 45-45-90\) triangle to find the length of the base and height. The formula for a \(\displaystyle 45-45-90\) triangle is \(\displaystyle a-a-a \sqrt{2}\)

Our \(\displaystyle 45-45-90\) triangle is: \(\displaystyle 4 \sqrt{2}m-4 \sqrt{2}m-8m\)

 

Plugging in our values, we get:

\(\displaystyle P = 4 \sqrt{2}m+4 \sqrt{2}m+8m = 8\sqrt{2}+8m\)

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

Triangle

Based on the information given above, what is the perimeter of triangle ABC?

Possible Answers:

\(\displaystyle 35+17.5\sqrt{2}\)

\(\displaystyle 52.5\sqrt{3}\)

\(\displaystyle 17.5+17.5\sqrt{3}\)

\(\displaystyle 52.5+17.5\sqrt{3}\)

\(\displaystyle 306.25\sqrt{3}\)

Correct answer:

\(\displaystyle 52.5+17.5\sqrt{3}\)

Explanation:

Triangle-solution

Consult the diagram above while reading the solution. Because of what we know about supplementary angles, we can fill in the inner values of the triangle. Angles A and B can be found by the following reductions:

A + 120 = 180; A = 60

B + 150 = 180; B = 30

Since we know A + B + C = 180 and have the values of A and B, we know:

60 + 30 + C = 180; C = 90

This gives us a 30:60:90 triangle. Now, since 17.5 is across from the 30° angle, we know that the other two sides will have to be √3 and 2 times 17.5; therefore, our perimeter will be as follows:

\(\displaystyle 17.5+2(17.5)+17.5\sqrt{3}=52.2+17.5\sqrt{3}\)

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