Math.acos()

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

Try it

// 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
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

undefined

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

See also