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4xy-[(x²+5xy-y²)-(x²+3xy-2y²)],其中x=2,y=-1求值，化简

分类: 作业答案 • 2022-09-27 17:56:45
问题描述：

4xy-[(x²+5xy-y²)-(x²+3xy-2y²)],其中x=2,y=-1
求值，化简

答

4xy-[(x²+5xy-y²)-(x²+3xy-2y²)]
=4xy-(x²+5xy-y²-x²-3xy+2y²)
=4xy-(2xy+y²)
=4xy-2xy-y²
=2xy-y²
=y(2x-y)
=(-1)x(2x2+1)
=-5

答

4xy-[(x²+5xy-y²)-(x²+3xy-2y²)]=4xy-(x²+5xy-y²-x²-3xy+2y²)=4xy-(2xy+y²)=2xy-y²=(2x-y)y=(2x2+1)x(-1)=-5

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