The ACOS function returns a numeric value in radians that approximates the arccosine of argument-1. The type of this function is numeric.
FUNCTION ACOS (argument-1)
|argument-1||Must be class numeric. The value of argument-1 must be greater than or equal to -1 and less than or equal to +1.|
The returned value is the approximation of the arccosine of argument-1 and is greater than or equal to zero and less than or equal to pi. This function will produce results accurate to only about 17 digits, even when argument-1 contains more than 18 digits (for example, if you have compiled your program for 31-digit support.)