如果(3x2-2)-(3x2-y)=-2,那么代数式(x+y)+3(x-y)-4(x-y-2)的值是(  ) A.4 B.20 C.8 D.-6

问题描述:

如果(3x2-2)-(3x2-y)=-2,那么代数式(x+y)+3(x-y)-4(x-y-2)的值是(  )
A. 4
B. 20
C. 8
D. -6

∵(3x2-2)-(3x2-y)=-2,
∴式子展开得:3x2-2-3x2+y=-2,
化简得:y=0,
∴将y=0代入代数式
(x+y)+3(x-y)-4(x-y-2),
=x+3x-4(x-2),
=4x-4x+8,
=8,
故选C.