# How to Use the Math.acos() Method in JavaScript

09/30/2021

Contents

In this article, you will learn how to use the Math.acos() method in JavaScript.

## Using the Math.acos() method in JavaScript

The Math.acos() method is a built-in function in JavaScript that returns the arccosine (in radians) of a given number. The input parameter must be a value between -1 and 1. If the parameter is outside of this range, the method will return NaN (not a number).

### Syntax

The syntax for using the Math.acos() method is:

``Math.acos(x)``

where x is the input parameter that represents the cosine of an angle.

### Examples

#### Using Math.acos() to calculate the arccosine of a number

``````const x = 0.5;
const arccosine = Math.acos(x);
console.log(arccosine); // 1.0471975511965979
``````

In this example, the input parameter is 0.5, which represents the cosine of an angle. The output is the arccosine of 0.5 in radians, which is approximately 1.0472.

#### Using Math.acos() with a value outside the range of -1 to 1

``````const x = 2;
const arccosine = Math.acos(x);
console.log(arccosine); // NaN
``````

In this example, the input parameter is 2, which is outside the range of -1 to 1. Therefore, the output is NaN.

#### Using Math.acos() with a negative value

``````const x = -0.7;
const arccosine = Math.acos(x);
console.log(arccosine); // 2.418858405776377
``````

In this example, the input parameter is -0.7, which represents the cosine of an angle. The output is the arccosine of -0.7 in radians, which is approximately 2.4189.

Note: The output of the Math.acos() method is always in radians. If you want to convert the result to degrees, you can use the following formula:

``degrees = radians * (180 / Math.PI)``

where radians is the output of the Math.acos() method.