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先化简,再求值:y(x+y)+(x+y)(x-y)-x2,其中x=-2,y=
1
2
人气:148 ℃ 时间:2020-05-27 17:49:54
解答
y(x+y)+(x+y)(x-y)-x2
=xy+y2+x2-y2-x2
=xy,
当x=-2,y=
1
2
时,原式=-2×
1
2
=-1.
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