###### (This is the legacy documentation for stable SDL2, the current stable version; [SDL3](https://wiki.libsdl.org/SDL3/) is the current development version.)
# SDL_acos

Use this function to compute arc cosine of `x`.

## Header File

Defined in [SDL_stdinc.h](https://github.com/libsdl-org/SDL/blob/SDL2/include/SDL_stdinc.h), but apps should _only_ `#include "SDL.h"`!

## Syntax

```c
double SDL_acos(double x);

```

## Function Parameters

|           |                                   |
| --------- | --------------------------------- |
| **x**     | floating point value, in radians. |

## Return Value

Returns arc cosine of `x`.

## Remarks

The definition of `y = acos(x)` is `x = cos(y)`.

Domain: `-1 <= x <= 1`

Range: `0 <= y <= Pi`

## Version

This function is available since SDL 2.0.2.

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[CategoryAPI](CategoryAPI), [CategoryAPIFunction](CategoryAPIFunction)