Math.acos()

The Math.acos() static method returns the inverse cosine (in radians) of a number. That is,

{{InteractiveExample("JavaScript Demo: Math.acos()")}}

```js interactive-example // Calculates angle of a right-angle triangle in radians function calcAngle(adjacent, hypotenuse) { return Math.acos(adjacent / hypotenuse); }

console.log(calcAngle(8, 10)); // Expected output: 0.6435011087932843

console.log(calcAngle(5, 3)); // Expected output: NaN

## Syntax

```js-nolint
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 {{jsxref("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()#

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#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• {{jsxref("Math.asin()")}}
• {{jsxref("Math.atan()")}}
• {{jsxref("Math.atan2()")}}
• {{jsxref("Math.cos()")}}
• {{jsxref("Math.sin()")}}
• {{jsxref("Math.tan()")}}
• CSS {{cssxref("acos()")}} function