###### (This is the documentation for SDL3, which is under heavy development and the API is changing! [SDL2](https://wiki.libsdl.org/SDL2/) is the current stable version!)
# SDL_acos

Compute the arc cosine of `x`.

## Header File

Defined in [<SDL3/SDL_stdinc.h>](https://github.com/libsdl-org/SDL/blob/main/include/SDL3/SDL_stdinc.h)

## Syntax

```c
double SDL_acos(double x);

```

## Function Parameters

|           |                      |
| --------- | -------------------- |
| **x**     | floating point value |

## Return Value

Returns arc cosine of `x`, in radians

## Remarks

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

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

Range: `0 <= y <= Pi`

This function operates on double-precision floating point values, use
[SDL_acosf](SDL_acosf) for single-precision floats.

This function may use a different approximation across different versions,
platforms and configurations. i.e, it can return a different value given
the same input on different machines or operating systems, or if SDL is
updated.

## Thread Safety

It is safe to call this function from any thread.

## Version

This function is available since SDL 3.0.0.

## Code Examples

```c
/* acos(x) = Pi/2 - asin(x) */
SDL_Log("acos(0):\t\t%f", SDL_acos(0.));
SDL_Log("Pi/2 - asin(0):\t%f", SDL_PI_D / 2 - SDL_asin(0));

/* acos(-x) = Pi  - acos(x) */
SDL_Log("acos(-(-1)):\t%f", SDL_acos(-(-1)));
SDL_Log("Pi - acos(-1):\t%f", SDL_PI_D - SDL_acos(-1));
```

## See Also

- [SDL_acosf](SDL_acosf)
- [SDL_asin](SDL_asin)
- [SDL_cos](SDL_cos)

----
[CategoryAPI](CategoryAPI), [CategoryAPIFunction](CategoryAPIFunction), [CategoryStdinc](CategoryStdinc)