And that's the Pythagorean theorem.

We could use the Pythagorean theorem.

Now that we know the Pythagorean theorem, let's actually use it.

So let's see if we can use the Pythagorean Theorem.

According to Pythagoras, the square of the hypotenuse...

So by the Pythagorean theorem, 9 squared plus 7 squared is going to be equal to c squared.

The Pythagorean theorem tells us that if and only if this is a right triangle, then a squared plus b squared is going to be equal to c squared.