Finding the perimeter of a triangle is quite an east task if you know the all three sides of the triangle.

Perimeter of a triangle is the sum of the lengths of all sides of a triangle. Sometimes you may come across a SAT Math question where length of one side of the triangle is missing. In such case, you have to find missing side before you add up all three sides to find the perimeter of a triangle.

Example 1

Find the perimeter of the triangle given below

Solution

Perimeter = sum of three sides

Perimeter = 5 + 8 + 15 = 28

Example 2

The triangle given below is an isosceles triangle. Find its perimeter.

Solution

Here length of one leg is missing. See it is an isosceles triangle; two of three legs must be equal. Now the question is what is the length of the third side of the triangle, 7 or 11? Observe that at top vertex is right angle. Hence in an isosceles triangle, legs whose meeting point forms right angle are of equal length. So the third side of the triangle is 7. Now find the perimeter of a triangle.

Perimeter = sum of three sides

Perimeter = 11 + 7 + 7 = 25

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**How to find the perimeter of a Triangle**