1.3 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 −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 pi.

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.