WorksheetFunction.Acos Method (Excel)
Returns the arccosine, or inverse cosine, of a number. The arccosine is the angle whose cosine is Arg1. The returned angle is given in radians in the range 0 (zero) to pi.
expression A variable that represents a WorksheetFunction object.
|Arg1||Required||Double||The cosine of the angle you want and must be from -1 to 1.|
If you want to convert the result from radians to degrees, multiply it by 180/PI() or use the Degrees method.