Web/JavaScript/Reference/Global objects/Math/acos

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

<math display="block">\forall x \in \lbrack{- 1};1\rbrack,\;\mathtt{\operatorname{Math.acos}(x)} = \arccos(x) = \text{the\ unique}\; y \in \lbrack 0;\pi\rbrack\,\text{such\ that}\;\cos(y) = x</math>

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.

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'Math.acos' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`acos`	Chrome Full support 1	Edge Full support 12	Firefox Full support 1	IE Full support 3	Opera Full support 3	Safari Full support 1	WebView Android Full support 1	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support 10.1	Safari iOS Full support 1	Samsung Internet Android Full support 1.0	nodejs Full support 0.1.100

Legend

Full support: Full support