ACOS function
Returns the arccosine of number, for example, the angle whose cosine is number.
Syntax
ACOS(number)
Remarks
The input value must be in the range -1 <= number <= 1, or a #NUM! error is returned. The resulting angle is in the range 0 <= angle <= PI radians (0 <= angle <= 180 degrees).
Example
ACOS(0)
Equals 90 deg.