ATAN2 function
Returns the arctangent, or inverse tangent, of the specified x and ycoordinates. The arctangent is the angle from the xaxis to a line containing the origin (0, 0) and a point with coordinates (x_num, y_num). The angle is given in radians between pi and pi, excluding pi.
Syntax
ATAN2(x_num,y_num)
X_num is the xcoordinate of the point.
Y_num is the ycoordinate of the point.
Remarks

A positive result represents a counterclockwise angle from the xaxis; a negative result represents a clockwise angle.

ATAN2(a,b) equals ATAN(b/a), except that a can equal 0 in ATAN2.

If both x_num and y_num are 0, ATAN2 returns the #DIV/0! error value.

To express the arctangent in degrees, multiply the result by 180/PI( ) or use the DEGREES function.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How to copy an example

Create a blank workbook or worksheet.

Select the example in the Help topic.
Note Do not select the row or column headers.
Selecting an example from Help

Press CTRL+C.

In the worksheet, select cell A1, and press CTRL+V.

To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.

