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# Math.acos()

The **`Math.acos()`** function returns the inverse cosine (in radians) of a number.

## 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).
