A long time ago, in ancient Greece, a brilliant guy named Pythagoras discovered something pretty amazing and useful.
In a right triangle the sum of the squares of the two legs equals the square of the hypotenuse.
So, let's break this down. If you square each side of the triangle, the sum of the areas of the two legs squared is equal to the hypotenuse squared.
Here you can see it with numbers:
The area of the two smaller squares is and
The area of the larger square is equal to
If you add the two smaller areas together, you get the area of the square of the hypotenuse
Look Out: Do not attempt this with obtuse or acute triangles! This awesome theorem only works for right triangles!