Rewrite with positive exponents. Assume that even roots are of nonnegative quantities and that all denominators are nonzero.

(2x^2y-^1)^-6

(2x^2y-^1)^-6

1/(2x^2y-^1)^6

1/(2^6 x^12 y^-6)

y^6 / 64x^12