WorksheetFunction.Acos (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.

If you want to convert the result from radians to degrees, multiply it by 180/PI() or use the Degrees method.

Acos (Arg1)

Arg1: The cosine of the angle you want, and must be from -1 to 1.

Dim dblArg1 As Double: dblArg1 = 
Dim dblAcos As Double
dblAcos = WorksheetFunction.Acos(Arg1:=dblArg1)