Returns the arctangent, or inverse tangent, of a number. The arctangent is the angle whose tangent is number. The returned angle is given in radians in the range pi/2 to pi/2.
Syntax
ATAN (number)
Number is the tangent of the angle you want.
Remark
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.
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A 
B 
Formula 
Description (Result) 
=ATAN(1) 
Arctangent of 1 in radians, pi/4 (0.785398) 
=ATAN(1)*180/PI() 
Arctangent of 1 in degrees (45) 
=DEGREES(ATAN(1)) 
Arctangent of 1 in degrees (45) 
