原式=(9x^-2y^-4)*(x^6y^6)/[1/(3xy^3)^2]
=(9x^-2y^-4)*(x^6y^6)*(3xy^3)^2
=(9x^-2y^-4)*(x^6y^6)*(9x^2y^6)
=9*9*x^(-2+6+2)*y^(-4+6+6)
=81x^6y^8