Contents|Index|Previous|Next acos, acosf [arc cosine] SYNOPSIS #include <math.h> double acos(double x); float acosf(float x); DESCRIPTION acos computes the inverse cosine (arc cosine) of the input value. Arguments to acos must be in the range of -1 to 1. acosf is identical to acos, except that it performs its calculations on floats. RETURNS acos and acosf return values in radians, in the range of 0 to . If x is not between -1 and 1, the returned value is NaN (not a number) the global variable errno is set to EDOM, and a DOMAIN error message is sent as standard error output. You can modify error handling for these functions using matherr.