ACOS(3)

NAME
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'.

SEE ALSO
acos is part of the library. The full documentation for is maintained as a Texinfo manual. If info and are properly installed at your site, the command

    info

will give you access to the complete manual.