Description
ACOS function calculates the arc cosine of @x; that is the value whose cosine is @x.  If @x  falls  outside  the range -1 to 1, ACOS fails and returns the NUM! error. The value it returns is in radians. This function is Excel compatible.
Examples
ACOS(0.1) equals 1.470629.
ACOS(-0.1) equals 1.670964.