已知A=2x^2+3ax-2x-1,B=-x^2+ax-1,且3A+6B的值与x无关,求a的值.

已知A=2x^2+3ax-2x-1,B=-x^2+ax-1,且3A+6B的值与x无关,求a的值.
已知A=2x^2+3ax-2x-1,B=-x^2+ax-1,且3A+6B的值与x无关,求a的值.

已知A=2x^2+3ax-2x-1,B=-x^2+ax-1,且3A+6B的值与x无关,求a的值.
3A+6B=3*(2x^2+3ax-2x-1)+6*(-x^2+ax-1)
=6x^2+9ax-6x-3-6x^2+6ax-6
=12ax-6x-9
与x无关,所以 12ax-6x=0,所以 a=1/2

3A+6B=3*(2x^2+3ax-2x-1)+6*(-x^2+ax-1)
=6x^2+9ax-6x-3-6x^2+6ax-6
=12ax-6x-9
与x无关，所以 12ax-6x=0，所以 a=1/2

签到:
3A+6B
=3(2x^2+3ax-2x-1)+6(-x^2+ax-1)
=(15a-6)x-9
because 3A+6B的值与x无关
so 15a-6=0
so a=0.4

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