##### Math trigonometric functions

- math.acos()
- math.acosh()
- math.asin()
- math.asinh()
- math.atan()
- math.atan2()
- math.atanh()
- math.cos()
- math.cosh()
- math.sin()
- math.sinh()
- math.sqrt()
- math.tan()
- math.tanh()

# math.acos()

Computes the principal value of the arc cosine of its argument *x*.

### Parameters

*x* - Floating point value. The value of *x* should be in the range -1 to 1 inclusive.

### Return Value

Upon successful completion, this function returns the arc cosine of *x* in the
range 0 to `math.PI`

radians inclusive.

If *x* is `math.NAN`

, a NaN will be returned.

If *x* is +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.

For finite values of x not in the range -1 to 1 inclusive, a domain error occurs and a NaN will be returned.

### Errors

If the *x* argument is finite and is not in the range -1 to 1 inclusive, or is `math.POS_INFINITY`

or `math.NEG_INFINITY`

, then `fastly.error`

will be set to `EDOM`

.

### Format

```
FLOAT
math.acos(FLOAT x)
```

### Examples

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declare local var.fo FLOAT;
set var.fo = math.cos(1.1); // Returns math.NAN
if (faslty.error) {
set resp.http.acos-error = faslty.error; // Returns "EDOM"
}