a2+b2=c2
the longest side of a right triangle
Because the Hypotinuse is the sum of the square of the other two sides. The sum of the square of the base plus the square of the height equals the slope.
The hypotenuse is the longest side on a right triangle. It is the side that is opposite (directly across from and facing) the 90-degree angle. If your drawing shows a 90-degree angle by labeling it with a small corner (box), then the point of the corner always points toward the side that is the hypotenuse.