text: (3x^2y^-4)^-3?   when you have (x^a)^b, that is the same as x^(a+b)  so you have: 3^-3 x^(2-3) y^(-4-3)  this simplifies to: 27^-1 x^-1 y^-7  now put all negative exponents in the denominator: .... 1 ---------- 27 x y^7