化简求值: [(x+2y)2-(x-2y)2-(x+2y)(x-2y)-4y2]÷2x,其中x=-2,y=1/2.
问题描述:
化简求值:
[(x+2y)2-(x-2y)2-(x+2y)(x-2y)-4y2]÷2x,其中x=-2,y=
. 1 2
答
[(x+2y)2-(x-2y)2-(x+2y)(x-2y)-4y2]÷2x,
=[(x2+4xy+4y2)-(x2-4xy+4y2)-(x2-4y2)-4y2]÷2x,
=(x2+4xy+4y2-x2+4xy-4y2-x2+4y2-4y2)÷2x,
=(-x2+8xy)÷2x,
=-
x+4y,1 2
当x=-2,y=
时,1 2
原式=-
×(-2)+4×1 2
=1+2=3.1 2