PHP atan() Function

The atan() function returns the arc tangent of arg as a numeric value between -Pi/2 and Pi/2 radians.

float atan ( float $arg )

Returns the arc tangent of arg in radians. atan() is the complementary function of tan(), which means that a==tan(atan(a)) for every value of a that is within atan()'s range.

Example -

ParameterDescription
argRequired. Specifies an argument to process

The arc tangent of arg in radians.