rewrite with positive exponents. assume that even roots are of nonnegative quantities and thst all denominators are nonzero.
1 )-3
-----
xy^3 )-3
everything times the negative power of 3 help please
(xy^3)^-3 = x^-3 * (y^3)^-3 = x^-3 * y^-9 = 1/x^3 * 1/y^9 = 1/(x^3 y^9)
or, doing it the other way,
(xy^3)^-3 = 1/(xy^3)^3 = 1/(x^3 y^9)
Not sure what the initial 1)-3 is all about, but what I posted above should get you going.