PHP. Руководство по PHP. 2005
atan2
atan2
Description
float atan2 (float y, float x)This function calculates the arc tangent of the two variables x and y. It is similar to calculating the arc tangent of y / x, except that the signs of both arguments are used to determine the quadrant of the result.
The function returns the result in radians, which is between -PI and PI (inclusive).
asinh
atan
