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.