---
title: math.cos
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/functions/math-trig/math-cos
---

```
FLOAT math.cos(FLOAT x)
```

**Available in:** all subroutines

Computes the cosine of its argument `x`, measured in radians.

## Parameters

`x` - Floating point value representing an angle in radians.

## Return Value

Upon successful completion, this function returns the cosine of `x`.

If `x` is `math.NAN`, a NaN will be returned.

If `x` is ±0, the value 1.0 will be returned.

If `x` is `math.POS_INFINITY` or
`math.NEG_INFINITY`, a domain error
occurs and a NaN will be returned.

## Errors

If the `x` argument is `math.POS_INFINITY`
or `math.NEG_INFINITY`, then
`fastly.error` will be set to `EDOM`.

## Example

```vcl
declare local var.fo FLOAT;

set var.fo = math.cos(math.PI_2);
```