Question

已知x+y=-4,xy=3,求5(½ xy+2y)+〔6x-( 2xy+y-3x)〕的值

Answer 1

5(½ xy+2y)+〔6x-( 2xy+y-3x)〕
=2.5xy＋10y＋6x－2xy－y＋3x
=½xy＋9y＋9x
=½×3＋9×﹙－4﹚
=－34.5

追问

若多项式2mx²-x平方+5x+8-（7x²-3y+5x）与x无关，求m²-［2m²-（5m-4）+4+m］的值

追答

2mx²-x²+5x+8-（7x²-3y+5x）
=﹙2m－1－7﹚x²＋3y＋8
多项式2mx²-x平方+5x+8-（7x²-3y+5x）与x无关
∴2m－1－7=0
m=4
m²-［2m²-（5m-4）+4+m］
=m²－[2m²－5m＋4＋4＋m]
=m²－2m²＋4m－8
=－m²＋4m－8
=－16＋16－8
=－8

Answer 2

5(½ xy+2y)+〔6x-( 2xy+y-3x)〕
=(5/2xy+10y)+(6x-2xy-y+3x)
=5/2xy+10y+6x-2xy-y+3x
=9x+9y+1/2xy
=9(x+y)+1/2xy
=9×(-4)+1/2×3
=-36+3/2
=-69/2

Answer 3

75/2