Math.acos

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

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

Syntax

Math.acos(x)

Parameters

x

A number.

Return value

The arccosine (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	Status	Comment
ECMAScript 1st Edition (ECMA-262)	Standard	Initial definition. Implemented in JavaScript 1.0.
ECMAScript 5.1 (ECMA-262) The definition of 'Math.acos' in that specification.	Standard
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Math.acos' in that specification.	Standard
ECMAScript 2017 Draft (ECMA-262) The definition of 'Math.acos' in that specification.	Draft

Browser compatibility

See also

• Math.asin()
• Math.atan()
• Math.atan2()
• Math.cos()
• Math.sin()
• Math.tan()