# 3.5.1.2.1 acos

## Description

The acos(x) function returns the inverse of the corresponding trigonometric function. x must be within -1 and 1 for acos, or a missing value is returned. Returned values are in radians, degrees or gradians, depending upon the system.math.angularunits object property (which can also be set in the Options dialog box).

## Syntax

double acos(double x)

## Parameter

x

is the value you want to get arccosine of. It must be in [-1, 1].

## Return

Returns the inverse of the corresponding trigonometric function.

## Example

aa = acos(1);
aa = ; //should return 0.