/sys$common/syshlp/helplib.hlb CC, Run-time functions, hypot  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Returns the square root of the sum of two squares of two arguments.
  For example:  sqrt(x*x + y*y).

  Syntax:

       #include <math.h>

       double hypot(double x, double y);