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

```
FLOAT math.tan(FLOAT x)
```

**Available in:** all subroutines

Computes the tangent 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 tangent of `x`.

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

If `x` is ±0, `x` will be returned.

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

If `x` is _subnormal_, a range error occurs and `x` will be returned.

If the result would cause an overflow, a range error occurs and `math.tan()`
will return `math.POS_HUGE_VAL` or
`math.NEG_HUGE_VAL`, with the same
sign as the result of the function.

## Errors

- If the `x` argument is
  `math.POS_INFINITY` or
  `math.NEG_INFINITY`, then
  `fastly.error` will be set to `EDOM`.
- If the `x` argument is _subnormal_ or if the result overflows, then
  `fastly.error` will be set to `ERANGE`.

## Example

```vcl
declare local var.fo FLOAT;

set var.fo = math.tan(math.PI_4);
```