The Pythagorean theorem is used for finding the distance between two points. You can consider the line from the origin to (12, 5) to be the hypotenuse of a right triangle with sides 12 and 5 (parallel to the x- and y-axes, respectively). Then the relation between these and the hypotenuse length is
... d² = 12² + 5² = 144 + 25 = 169
... d = √169 = 13
The point (12, 5) is 13 units from the origin.
