# math/acos Arc cosine; returns an angle in radians. ## Syntax

[math/acos $x]

## Parameters - `$x` — Value in the range [-1, 1] ## Examples

[math/acos 1]    # 0
[math/acos 0]    # 1.5707963267948966 (π/2)

## Returns Number — angle in radians, in the range [0, π]. ## See Also `math/asin`, `math/atan`, `math/cos`