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FreeBSD 11.0 - man page for acos (freebsd section 3)

ACOS(3) 						   BSD Library Functions Manual 						   ACOS(3)

NAME
acos, acosf, acosl -- arc cosine functions
LIBRARY
Math Library (libm, -lm)
SYNOPSIS
#include <math.h> double acos(double x); float acosf(float x); long double acosl(long double x);
DESCRIPTION
The acos(), acosf(), and acosl() functions compute the principal value of the arc cosine of x.
RETURN VALUES
These functions return the arc cosine in the range [0, pi] radians. If: |x| > 1, acos(x) raises an invalid exception and returns an NaN.
SEE ALSO
asin(3), atan(3), atan2(3), cos(3), cosh(3), fenv(3), math(3), sin(3), sinh(3), tan(3), tanh(3)
STANDARDS
The acos(), acosf(), and acosl() functions conform to ISO/IEC 9899:1999 (``ISO C99'').
BSD
July 31, 2008 BSD