rewrite with positive exponents. Assume that even roots are nonnegative quanities and that all denominators are nonzero.
[3/ua^2)^-4
(3/ua^2)^-4 =
1 / (3/ua^2)^4 =
1 / (81/u^4a^8) =
1 * (u^4a^8/81) =
(u^4a^8) / 81.
[3/ua^2)^-4
1 / (3/ua^2)^4 =
1 / (81/u^4a^8) =
1 * (u^4a^8/81) =
(u^4a^8) / 81.