ab=8,a-2b=4.求(a^2-4b^2)(a^2b+2ab^2)
问题描述：
ab=8,a-2b=4.求(a^2-4b^2)(a^2b+2ab^2)
答
(a^2-4b^2)(a^2b+2ab^2)
=（a+2b)(a-2b)[ab(a+2b)]
=(a+2b)^2(a-2b)ab
(a+2b)^2=(a-2b)^2+8ab=16+64=80
则a+2b=±4根号5
则原式=±4根号5*4*8=±128根号5