---
layout: stdlib-reference
---
# acos
## Description
Arc cosine. Returns the angle whose cosine is the specified number.
## Signature
T acos<T>(T x)
where T : __BuiltinFloatingPointType;
vector<T, N> acos<T, N:int>(vector<T, N> x)
where T : __BuiltinFloatingPointType;
matrix<T, N, M> acos<T, N:int, M:int>(matrix<T, N, M> x)
where T : __BuiltinFloatingPointType;
## Generic Parameters
#### T: [\_\_BuiltinFloatingPointType](../interfaces/0_builtinfloatingpointtype-029hm/index.html)
#### N : int
#### M : int
## Parameters
#### x : [T](acos.html#typeparam-T)
The cosine value.
#### x : [vector](../types/vector/index.html)\<[T](../types/vector/index.html#typeparam-T), [N](../types/vector/index.html#decl-N)\>
The cosine value.
#### x : [matrix](../types/matrix/index.html)\<[T](../types/matrix/t-0.html), [N](../types/matrix/index.html#decl-N), [M](../types/matrix/index.html#decl-M)\>
The cosine value.
## Return value
The angle in radians, in the range of [0, pi].
## Availability and Requirements
Defined for the following targets:
#### hlsl
Available in all stages.
#### glsl
Available in all stages.
#### cpp
Available in all stages.
#### cuda
Available in all stages.
#### metal
Available in all stages.
#### wgsl
Available in all stages.
#### spirv
Available in all stages.