math:acos
Returns the arc cosine of the argument, the result being in the range zero to
            +π radians.
acos($arg as xs:double?) ➔ xs:double?
Arguments  | |||
  | $arg  | xs:double?  | The supplied angle in radians  | 
Result  | xs:double?  | ||
Namespace
http://www.w3.org/2005/xpath-functions/math
Links to W3C specifications
XPath 3.0 Functions and Operators
XPath 3.1 Functions and Operators
Notes on the Saxon implementation
Implemented since Saxon 9.3; available whether or not support for XPath 3.0 is enabled.
          Saxon also (for compatibility) implements the function math:acos() in namespace
            http://exslt.org/math.