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.