Returns the arccosine, or inverse cosine, of a number. The arccosine is the angle whose cosine is number. The returned angle is given in radians in the range 0 (zero) to pi.
Syntax
ACOS(number)
Number is the cosine of the angle you want and must be from 1 to 1.
Remark
If you want to convert the result from radians to degrees, multiply it 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) 
=ACOS(0.5) 
Arccosine of 0.5 in radians, 2*pi/3 (2.094395) 
=ACOS(0.5)*180/PI() 
Arccosine of 0.5 in degrees (120) 
=DEGREES(ACOS(0.5)) 
Arccosine of 0.5 in degrees (120) 
