XPath/XQuery acos function


Returns the arc cosine of the argument.


$arg as xs:double?
) as xs:double?


This function is deterministic, context-independent, and focus-independent.


If $arg is the empty sequence, the function returns the empty sequence.

Otherwise the result is the arc cosine of $arg, as defined in the specification of the acos function applied to 64-bit binary floating point values. The result is in the range zero to +π radians.


The expression math:acos(()) returns ().

The expression math:acos(0) returns 1.5707963267948966e0.

The expression math:acos(-0.0e0) returns 1.5707963267948966e0.

The expression math:acos(1.0e0) returns 0.0e0.

The expression math:acos(-1.0e0) returns 3.141592653589793e0.

The expression math:acos(2.0e0) returns xs:double('NaN').

The expression math:acos(xs:double('NaN')) returns xs:double('NaN').

The expression math:acos(xs:double('INF')) returns xs:double('NaN').

The expression math:acos(xs:double('-INF')) returns xs:double('NaN').


The treatment of the invalidOperation exception is defined in .

If $arg is NaN, or if its absolute value is greater than one, then the result is NaN.

In other cases the result is an xs:double value representing an angle θ in radians in the range 0 <= θ <= + π.