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.

A 
B 
Formula 
Description (Result) 
=ATAN2(1, 1) 
Arctangent of the point 1,1 in radians, pi/4 (0.785398) 
=ATAN2(1, 1) 
Arctangent of the point 1,1 in radians, 3*pi/4 (2.35619) 
=ATAN2(1, 1)*180/PI() 
Arctangent of the point 1,1 in degrees (135) 
=DEGREES(ATAN2(1, 1)) 
Arctangent of the point 1,1 in degrees (135) 
