(2x)的3n次方然后再二次方就是2x的6n次方，等于4的3n次方乘以x的6n次方，除以4x的4n次方就是5除以4的n次方
[2x^(3n)]^2÷4x^(4n)=4x^(6n)÷4x^(4n)=x^(2n)=5
(2x^3n)^2/4x^4n=4x^6n/4x^4n=x^2n=5
