> ## Documentation Index
> Fetch the complete documentation index at: https://axiom.co/docs/llms.txt
> Use this file to discover all available pages before exploring further.

<AgentInstructions>

## Submitting Feedback

If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback:

POST https://axiom.co/docs/feedback

```json
{
  "path": "/apl/scalar-functions/mathematical-functions/asin",
  "feedback": "Description of the issue"
}
```

Only submit feedback when you have something specific and actionable to report.

</AgentInstructions>

# asin

> This page explains how to use the asin function in APL.

Use the `asin` function in APL to compute the arc sine (inverse sine) of a numeric expression. The function returns the angle, in radians, whose sine equals the input value. The input must be in the range \[-1, 1]; values outside this range return `null`.

`asin` is useful when you work with normalized ratios or rates and need to map them to angular values. For example, you can use `asin` to encode success or error rates as phase angles for cyclic signal analysis.

## For users of other query languages

If you come from other query languages, this section explains how to adjust your existing queries to achieve the same results in APL.

<AccordionGroup>
  <Accordion title="Splunk SPL users">
    In Splunk SPL, `asin()` is available in the `eval` command with the same behavior: it returns the arc sine in radians for an input in \[-1, 1].

    <CodeGroup>
      ```sql Splunk example theme={null}
      | eval angle = asin(normalized_rate)
      ```

      ```kusto APL equivalent theme={null}
      ['sample-http-logs']
      | extend angle = asin(normalized_rate)
      ```
    </CodeGroup>
  </Accordion>

  <Accordion title="ANSI SQL users">
    In ANSI SQL, `ASIN()` is a standard mathematical function. It accepts a value in \[-1, 1] and returns the arc sine in radians.

    <CodeGroup>
      ```sql SQL example theme={null}
      SELECT ASIN(normalized_rate) AS angle FROM logs
      ```

      ```kusto APL equivalent theme={null}
      ['sample-http-logs']
      | extend angle = asin(normalized_rate)
      ```
    </CodeGroup>
  </Accordion>
</AccordionGroup>

## Usage

### Syntax

```kusto theme={null}
asin(x)
```

### Parameters

| Name | Type | Required | Description                          |
| ---- | ---- | -------- | ------------------------------------ |
| `x`  | real | Yes      | A real number in the range \[-1, 1]. |

### Returns

* The arc sine of `x` in radians, in the range \[-π/2, π/2].
* `null` if `x` \< -1 or `x` > 1.

## Example

Use `asin` to compute the arcsine of a value and return the angle in radians.

**Query**

```kusto theme={null}
print result = asin(0.5)
```

[Run in Playground](https://play.axiom.co/axiom-play-qf1k/query?initForm=%7B%22apl%22%3A%20%22print%20result%20%3D%20asin%280.5%29%22%7D)

**Output**

| result |
| ------ |
| 0.5236 |

## List of related functions

* [acos](/apl/scalar-functions/mathematical-functions/acos): Returns the arc cosine. Use it when the cosine encoding is more appropriate for your data.
* [atan](/apl/scalar-functions/mathematical-functions/atan): Returns the arc tangent. Use it when the input is not bounded to \[-1, 1].
* [sin](/apl/scalar-functions/mathematical-functions/sin): Returns the sine. Use it to apply the forward transformation before using `asin` as the inverse.
* [radians](/apl/scalar-functions/mathematical-functions/radians): Converts degrees to radians. Use it if your angle data is in degrees before passing it to `asin`.
* [degrees](/apl/scalar-functions/mathematical-functions/degrees): Converts radians to degrees. Use it to convert the `asin` result into degrees.