`double hypot(double __x, double __y)`

The hypot() function returns *sqrt(__x*__x +
__y*__y)*. This is the length of the hypotenuse of a right triangle with
sides of length *__x* and *__y*, or the distance
of the point (*__x*, *__y*) from the origin. Using
this function instead of the direct formula is wise, since the error is much smaller. No
underflow with small *__x* and *__y*. No overflow
if result is in range.