已知整式A=2x2+3xy+2y-1 B=x2-xy+x-1/2. 当x=y=-2时,求A-2B的值

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已知整式A=2x2+3xy+2y-1 B=x2-xy+x-1/2.A-2B=2x2+3xy+2y-1-2x2+2xy-2x+1=5xy+2y-2x
x=y=-2=20-4+4=20...

千问 | 2012-11-6 21:18:23 | 显示全部楼层

解：∵整式A=2x2+3xy+2y-1 B=x2-xy+x-1/2,
∴A-2B=2x2+3xy+2y-1 -2﹙x2-xy+x-1/2﹚,
=2x2+3xy+2y-1 -2x2+2xy-2x+1
=5XY+2Y-2X把x=y=...

千问 | 2012-11-6 21:18:23 | 显示全部楼层

∵A=2x2+3xy+2y-1 B=x2-xy+x-1/2. ∴A-2B=2x2+3xy+2y-1-2(x2-xy+x-1/2)=2x2+3xy+2y-1-2x2+2xy-2x+1=5xy+2(y-x) 当x=y=-2时,原式=5×（-2）×（-2）+2【（-2）-（-2）】=20+0=20...

千问 | 2012-11-6 21:18:23 | 显示全部楼层

A-2B=5xy+2y-2x,将数字带入得结果20...

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