ACOS Section: Linux Programmer's Manual (3) Updated: June 8, 2025 Index   NAME acos - arc cosine function   SYNOPSIS #include <math.h> double acos(double x);   DESCRIPTION The acos() function calculates the arc cosine of x; that is the value whose cosine is x. If x falls outside the range -1 to 1, acos() fails and errno is set.   RETURN VALUE The acos() function returns the arc cosine in radians and the value is mathematically defined to be between 0 and PI (inclusive).   ERRORS EDOM x is out of range.   CONFORMING TO SVID 3, POSIX, BSD 4.3, ISO 9899   SEE ALSO   Index NAME SYNOPSIS DESCRIPTION RETURN VALUE ERRORS CONFORMING TO SEE ALSO This document was created by using the manual pages. Time: 11:58:02 GMT, March 24, 2025