原式=(x^m)^3除以(x^n)^2 = 2^3/3^2 =8/9
x^(3m-2n)=x^3m/x^2n=(x^m)^3/(x^n)^2=2^3/3^2=8/9
x^(3m-2n)=x^(3m) / x^(2n) =2^3 / 3^2 = 8/9
