已知x+y分之xy=3求-2x+3xy-2y分之3x-5xy+3y的值

题目

已知x+y分之xy=3求-2x+3xy-2y分之3x-5xy+3y的值

答案

∵(x+y)分之xy=3
∴xy=3(x+y)
∴(-2x+3xy-2y)分之(3x-5xy+3y)
=[-2(x+y)+9(x+y)]分之[3(x+y)-15(x+y)]
=[7(x+y)]分之[-12(x+y)]
=-7分之12
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