计算a^2n+1-6a^2n+9a^2n-1/a^2-9除以a^n+1+4a^n+4a^n-1/a^2-4

a^2n+1-6a^2n+9a^2n-1/a^2-9除以a^n+1+4a^n+4a^n-1/a^2-4
=[a^(2n-1)*(a-3)^2]/(a^2-9) * （a^2-4)/[a^(n-1)*(a+2)^2]
=[a^n*(a-3)(a-2)]/(a+3)(a+2)