get angle and radian between two points

The atan2 function is an extended version of the trigonometric inverse tangent function.
In the figure below, tan?=y/x, so tan-1y/x=?. The atan2 function just calculates tan-1y/x with y and x as separate parameters.
The reason it does so is to give a more accurate answer: since the tangent function is periodic,
there are multiple values of x and y that would appear to have the same angle (but do not).
Also, atan2 provides the correct values when y/x is undefined, such as at p/2.
%Input O-(x1,y1) and P-(x2,y2)points
%Output Angle
%devloper Er.Abbas Manthiri S
%Email-abbasmanthiribe@gmail.com