double hypot(double x, double y);

**hypot** computes the square root of the sum of the squares of
**x** and **y**, **sqrt**(**x*****x** + **y*****y**), without undue overflow or underflow.
If **x** and **y** are the lengths of the sides of a right-angled triangle,
then **hypot** computes the length of the hypotenuse.

If **x** or **y** is +∞ or ?∞, **hypot** returns ∞.

If **x** or **y** is NaN, **hypot** returns NaN.