# ACOS

**The ACOS function returns the arccosine (in radians) of a given number.**

This function takes a single [Number](../../variable-data-types/the-number-variable-data-type) as input. It outputs another Number: the arccossin, in radians, of the given number.

#### Declaration

```javascript
ACOS(number) -> arccosine
```

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#### Parameters

**number** (required, type: _Number_) Any number.

#### Return Values

**arccosine** (type: _Number_) The arccosine, in radians, of the given number.

#### Examples

The following example returns the arccosine of 0.5. Note that the arccossine of one half is sixty degrees, or _π/&#x33;_&#x72;adians, but the ACOS function doesn't output an angle in degrees or in radians in terms of pi. Rather, it provides a numerical estimation of the angle in radians:

```javascript
ACOS(0.5) -> 1.0471975511965979
```

To calculate the arctangent in degrees, the ACOS function must be used in tandem with the [DEGREES](degrees) function, such as in the following example. Note that the output is not exactly 60, but it is extremely close. This is the result of small rounding errors:

```javascript
DEGREES(ACOS(0.5)) -> 60.00000000000001
```

ACOS can also be used in tandem with the [PI](pi) function to provide insight into how the angle in radians relates to terms of pi, such as in the following example. Note again that, due to small rounding errors, the output is not a precise numerical estimation of _1/3_:

```javascript
ACOS(0.5)/PI() -> 0.33333333333333337
```
