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

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.

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**Authoritative source**: BUSMASTER DITA help source `acos.dita`, compiled into `BUSMASTER.CHM` with the application.