问题 解答题
化简求值:
[(x+2y)2-(x-2y)2-(x+2y)(x-2y)-4y2]÷2x,其中x=-2,y=
1
2
答案

[(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,

=-

1
2
x+4y,

当x=-2,y=

1
2
时,

原式=-

1
2
×(-2)+4×
1
2
=1+2=3.

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