# Function acos Calculate the inverse cosine of a value. For matrices, the function is evaluated element wise. ## Syntax ```js math.acos(x) ``` ### Parameters Parameter | Type | Description --------- | ---- | ----------- `x` | number | BigNumber | Complex | Array | Matrix | Function input ### Returns Type | Description ---- | ----------- number | BigNumber | Complex | Array | Matrix | The arc cosine of x ### Throws Type | Description ---- | ----------- ## Examples ```js math.acos(0.5) // returns number 1.0471975511965979 math.acos(math.cos(1.5)) // returns number 1.5 math.acos(2) // returns Complex 0 + 1.3169578969248166 i ``` ## See also [cos](cos.md), [atan](atan.md), [asin](asin.md)