已知x+y=3,xy=1,求代数式5xy+4x+7y+6x-3xy-4xy+3y的值.
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已知x+y=3,xy=1,求代数式5xy+4x+7y+6x-3xy-4xy+3y的值.
5xy+4x+7y+6x-3xy-4xy+3y
=5xy-3xy-4xy+4x+6x+7y+3y
=(5-3-4)xy+(4+6)x+(7+3)y
=-2xy+10x+10y
=-2xy+10(x+y)
因为x+y=3,xy=1
所以原式=-2xy+10(x+y)
=-2×1+10×3
=-2+30
=28
因为5xy+4x+7y+6x-3xy-4xy+3y=-2xy+10x+10y=-2xy+10(x+y)
当x+y=3,xy=1时,原式=-2x1+10x3=28
5xy+4x+7y+6x-3xy-4xy+3y=10x+10y-2xy=10(x+y)-2xy=10*3-2=28
5xy+4x+7y+6x-3xy-4xy+3y先简化
=10x+10y-2xy
=10(x+y)-2xy
把x+y=3,xy=1代入
求得5xy+4x+7y+6x-3xy-4xy+3y=28
原式 =(5xy-3xy-4xy)+【(4x+6x)+(7y+3y)】
=-2xy+10(x+y)
因为x+y=3,xy=1
所以原式=-2+10*3=28
5xy+4x+7y+6x-3xy-4xy+3y
=5xy-3xy-4xy+4x+6x+7y+3y
=(5-3-4)xy+(4+6)x+(7+3)y
=-2xy+10x+10y
=-2xy+10(x+y)
因为x+y=3,xy=1
所以原式=-2xy+10(x+y)
=-2×1+10×3
=-2+30
=28
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