问题
选择题
若
|
答案
∵
-1 x
=1 y
=3，即x-y=-3xy，-(x-y) xy
∴原式=5(x-y)+3xy 3(x-y)-xy
=-15xy+3xy -9xy-xy
=-12xy -10xy
=
．6 5
故选C．
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若
|
∵
-1 x
=1 y
=3，即x-y=-3xy，-(x-y) xy
∴原式=5(x-y)+3xy 3(x-y)-xy
=-15xy+3xy -9xy-xy
=-12xy -10xy
=
．6 5
故选C．