> For the complete documentation index, see [llms.txt](https://mariadb.com/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mariadb.com/docs/server/reference/sql-functions/numeric-functions/acos.md).

# ACOS

## Syntax

```bnf
ACOS(X)
```

## Description

Returns the arc cosine of `X`, that is, the value whose cosine is `X`. Returns `NULL` if `X` is not in the range `-1` to `1`.

## Examples

```sql
SELECT ACOS(1);
+---------+
| ACOS(1) |
+---------+
|       0 |
+---------+

SELECT ACOS(1.0001);
+--------------+
| ACOS(1.0001) |
+--------------+
|         NULL |
+--------------+

SELECT ACOS(0);
+-----------------+
| ACOS(0)         |
+-----------------+
| 1.5707963267949 |
+-----------------+

SELECT ACOS(0.234);
+------------------+
| ACOS(0.234)      |
+------------------+
| 1.33460644244679 |
+------------------+
```

<sub>*This page is licensed: GPLv2, originally from*</sub> [<sub>*fill\_help\_tables.sql*</sub>](https://github.com/MariaDB/server/blob/main/scripts/fill_help_tables.sql)

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