(ACOS(arg))
Computes the arccosine of arg where arg is in the range -1 to 1. The result is an angle in radians between 0 and pi (where pi = 3.14159265358979).
In the following example, the value of vacos is 2.094395, the arccosine of -0.5.
SET VAR vacos = (ACOS(-0.5))
