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(3x²-2)-(3x²-y)=-2
3x²-2-3x²-y=-2
3x²-3x²-y= -2+2
-y=0
Y=0
(x+y)+3(x-y)-4(x-y-2)
=x+y+3x-3y-4x+4y+8
=(1+3-4)x+(1-3+4)y+8
=2y+8
把y=0代入,得
原式=2*0+8=8

那么代数式(x+y)+3(x-y)-4(x-y-2)的值是0

(x+y)+3(x+y)-4(x-y-2)=8(y+1)
由已知可得
y=0
所以原式=8