# How Do You Find the Hypotenuse of an Isosceles Triangle, Given Two Lengths?

By Staff WriterLast Updated Mar 27, 2020 11:18:22 PM ET

Use the Pythagorean theorem to calculate the hypotenuse of a right triangle. A right triangle is a type of isosceles triangle. The hypotenuse is the side of the triangle opposite the right angle.

1. Make certain the triangle is a right triangle

The Pythagorean theorem can only be used with isosceles triangles that are right triangles. This means one of the angles must be 90 degrees. If it's not, the theorem cannot be used.

2. Write down the Pythagorean theorem

The Pythagorean theorem states that the square of the hypotenuse is equal to the sum of the squares of the two shorter legs. It's often written as h squared equals a squared plus b squared.

3. Insert the numbers

Replace a and b in the equation with the lengths of the two sides. As an example, let a = 3 and b = 4.

4. Square both of the lengths

To find the square of a number, multiply it by itself. For example, to find the square of 3, multiply 3 by 3 to get 9. For 4, multiply 4 by 4 to get 16.