若n为正整数,且x^2n=7,求(3x^3n)^2-4(x^2)^2n的值,拜托各位好人们了,帮帮我吧,行行好啊~~

问题描述:

若n为正整数,且x^2n=7,求(3x^3n)^2-4(x^2)^2n的值,拜托各位好人们了,帮帮我吧,行行好啊~~

(3x^3n)^2-4(x^2)^2n
=9x^6n-4x^4n
=9*(x^2n)^3-4*(x^2n)^2
=9*7^3-4*7^2
=7^2*(9*7-4)
=49*59
=2891