# How to Make Geometry Your Best Friend (Part 2) The Pythagorean Theorem is one of the most important theorems that you’ll come across in geometry. However, before we delve into it, first let’s look at the definition of a right triangle.

### A right triangle is a triangle in which one angle is a right angle (90-degree angle).

The Pythagorean Theorem states that the square of the hypotenuse (the side opposite the right angle) is equal to the sum f the square of both sides. It’s mathematically expressed as a² + b² = c². The letters represent the side lengths of a right triangle. The c is the length of the hypotenuse and the a and b are the lengths of the other two sides or legs. The Pythagorean Theorem should always be the first thing you think of when you see a right triangle! Remember, the Pythagorean theorem ONLY applies to right triangles. It does NOT apply to triangles that don’t have right angles.

Read Part 3 of this series to see how Pythagorean Triples will make your life easier when dealing with right triangles. For additional help, check out Brightstorm geometry.