问题 选择题

(x+y)(-x-y)的计算结果是(  )

A.-x2-y2

B.-x2+y2

C.-x2+2xy+y2

D.-x2-2xy-y2

答案

(x+y)(-x-y),

=-(x+y)2

=-(x2+2xy+y2),

=-x2-2xy-y2

故选D.

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