4xy-((x^2+5xy-y^2)-(x^2+3xy-2y^2))
=4xy-(x²+5xy-y²)+(x²+3xy-2y²)
=4xy-x²-5xy+y²+x²+3xy-2y²
=2xy-y²
当x=2,y=-1时
原式=-4-1=-5
4xy-((x^2+5xy-y^2)-(x^2+3xy-2y^2)),其中x=2,y=-1.
4xy-((x^2+5xy-y^2)-(x^2+3xy-2y^2)),其中x=2,y=-1.
数学人气：544 ℃时间：2019-12-23 15:52:27
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