A-2B
=2x^2-3ax+2x-1-2(x^2+ax+3x-2)
=2x^2-3ax+2x-1-2x^2-2ax-6x+4
=-3ax+2x-2ax-6x+3
=-5ax-4x+3
因为与X无关
则
-5a-4=0
-5a=4
a=-4/5