解：?$ (1)$?原式?$=3×(3^3)^{m}\div (3^2)^{m}$?
?$ =3×3^{3m}\div 3^{2m}$?
?$=3^{1 + 3m-2m}$?
?$=3^{m + 1}$?
?$ $?因為?$3^{m + 1}=3^{16}，$?
所以?$m + 1 = 16，$?即?$m = 15$?
?$ (2)a^{3x-2y}=a^{3x}\div a^{2y}=(a^{x})^3\div (a^{y})^2$?
?$=(-2)^3\div 3^2=-\frac {8}{9}$?
?$ (3)$?原式?$=9(x^{2n})^3-4(x^{2n})^2$?
?$=9×4^3-4×4^2$?
?$= 512$?
