Math.acos()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The Math.acos() static method returns the inverse cosine (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

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Syntax

js
Math.acos(x)

Parameters

x

A number between -1 and 1, inclusive, representing the angle's cosine value.

Return value

The inverse cosine (angle in radians between 0 and π, inclusive) of x. If x is less than -1 or greater than 1, returns NaN.

Description

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()

js
Math.acos(-2); // NaN
Math.acos(-1); // 3.141592653589793 (π)
Math.acos(0); // 1.5707963267948966 (π/2)
Math.acos(0.5); // 1.0471975511965979 (π/3)
Math.acos(1); // 0
Math.acos(2); // NaN

Specifications

Specification
ECMAScript® 2025 Language Specification
# sec-math.acos

Browser compatibility

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See also