* The arctangent of an angle is the inverse of the TAN function.
* ATAN2(x_num , y_num) equals ATAN(y_num / x_num), except that "x_num" can equal 0 in ATAN2.
* The arctangent is the angle from the x-axis to a line containing the origin (0, 0) and a point with coordinates ("x_num", "y_num").
* If "x_num" = 0 and "y_num" = 0, then #DIV/0! is returned.
* The returned angle is given in radians between -PI and PI (excluding -PI).
* A positive result represents an anti-clockwise angle (from the x-axis).
* A negative result represents a clockwise angle (from the x-axis).
* If your argument is in degrees, multiple it by PI/180 to convert it to radians.
* If you want to convert the result from radians to degrees, multiply it by 180/PI.
* You can use the DEGREES function to convert from radians to degrees.
* For a working example refer to the Trigonometry page.
* For the Microsoft documentation refer to support.office.com.