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.
(x+y)(-x-y)的计算结果是( )
A.-x2-y2
B.-x2+y2
C.-x2+2xy+y2
D.-x2-2xy-y2
(x+y)(-x-y),
=-(x+y)2,
=-(x2+2xy+y2),
=-x2-2xy-y2.
故选D.