NAME

acos, acosf, acosl —

arc cosine functions

LIBRARY

Math Library (libm, -lm)

#include <math.h>

double
acos(double x);

float
acosf(float x);

long double
acosl(long double x);

The acos(), acosf(), and acosl() functions compute the principal value of the arc cosine of x.

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.

The acos(), acosf(), and acosl() functions conform to ISO/IEC 9899:1999 (“ISO C99”).