ACOS takes a numeric value and returns the inverse (arc) of its cosine as a floating point number. The value of numeric-expression must be a signed decimal number ranging from 1 to -1 (inclusive). A number outside of this range causes a runtime error, generating an SQLCODE -400 (fatal error occurred). ACOS returns NULL if passed a NULL value. ACOS treats nonnumeric strings, including the empty string (''), as the numeric value 0.
ACOS returns a value with a precision of 19 and a scale of 18.
ACOS can only be used as an ODBC scalar function (with the curly brace syntax).
You can use the DEGREES function to convert radians to degrees. You can use the RADIANS function to convert degrees to radians.