# Math.acos()

The Math.acos() function returns the arccosine (in radians) of a number, that is

$∀ x ∊ [ - 1 ; 1 ] , Math.acos ( x ) = arccos ( x ) = the unique y ∊ [ 0 ; π ] such that cos ( y ) = x \forall x \in [{-1};1],\;\mathtt{\operatorname{Math.acos}(x)} = \arccos(x) = \text{ the unique } \; y \in [0; \pi] \, \text{such that} \; \cos(y) = x$

## Syntax

Math.acos(x)

### Parameters

x
A number representing a cosine, where x is between -1 and 1.

### Return value

The arccosine (angle in radians) of the given number if it's between -1 and 1; otherwise, NaN.

## Description

The Math.acos() method returns a numeric value between 0 and π radians for x between -1 and 1. If the value of x is outside this range, it returns NaN.

Because acos() is a static method of Math, you always use it as Math.acos(), rather than as a method of a Math object you created (Math is not a constructor).

## Examples

### Using Math.acos()

Math.acos(-2);  // NaN
Math.acos(-1);  // 3.141592653589793
Math.acos(0);   // 1.5707963267948966
Math.acos(0.5); // 1.0471975511965979
Math.acos(1);   // 0
Math.acos(2);   // NaN


For values less than -1 or greater than 1, Math.acos() returns NaN.

## Browser compatibility

BCD tables only load in the browser