x^9y^4除以(x²y)^3除以x²
=x^9y^4÷x^6y³÷x²
=x³y÷x²
=xy
a^2m除以a^2m-3*(-a)²
=a^2m÷a^(2m-3)×a²
=a^(2m-2m+3+2)
=a^5