先化简,再求值:(x+2y)(x-2y)(x2-4y2),其中x=2,y=-1.
问题描述:
先化简,再求值:(x+2y)(x-2y)(x2-4y2),其中x=2,y=-1.
答
(x+2y)(x-2y)(x2-4y2)
=(x2-4y2)(x2-4y2)
=x4-16y4,
当x=2,y=-1时,原式=24-16×(-1)4=0.