 # JavaScript Math acos()

In this tutorial, you will learn about the JavaScript Math.acos() method with the help of examples.

The `acos()` method calculates the arc-cosine (inverse of cosine) of the specified angle and returns it.

### Example

``````let value = Math.acos(0.45);
console.log(value);

// Output: 1.1040309877476002``````

## acos() Syntax

The syntax of the `Math.acos()` method is:

``Math.acos(angle)``

Here, `acos()` is a static method. Hence, we are accessing the method using the class name, `Math`.

## acos() Parameter

The `acos()` method takes a single parameter:

• `angle` (radians) - in range -1 to 1 whose arc-cosine is to be calculated

## acos() Return Value

The `acos()` method returns:

• arc-cosine value of the `angle`
• NaN (Not a Number) for argument greater than 1 or less than -1 or non-numeric

## Example 1: Math.acos() with Arguments Between -1 and 1

``````// arc-cosine of negative number
let number1 = Math.acos(-1);
console.log(number1);

// arc-cosine of positive number
let number2 = Math.acos(0.5);
console.log(number2);

// Output:
// 3.141592653589793
// 1.0471975511965979``````

In the above example, the `Math.acos()` method computes the arc-cosine of

• `-1` (negative number) - results in 3.141592653589793
• `0.5` (positive number) - results in 1.0471975511965979

## Example 2 : Math.acos() with Arguments Not Between -1 and 1

``````// argument less than -1
let number1 = Math.acos(-3);
console.log(number1);
// Output: NaN

// argument greater than 1
let number2= Math.acos(32);
console.log(number2);
// Output: NaN    ``````

Here, we have used the `Math.acos()` method with values -3 (less than -1) and 32 (greater than 1). For both values, we get NaN as output.

## Example 3: Math.acos() with Non-Numeric Argument

``````let string = "Harry";

// acos() with a string argument
let value = Math.acos(string);
console.log(value);

// Output:
// NaN``````

In the above example, we have used `Math.acos()` with a string value, `"Harry"`. Hence, we get NaN as the output.