(2x^2+3ax-y)-2(bx^2-3x+2y-1) =2x+3ax-y-2bx+6x-4y+2 =(2-2b)x+(3a+6)x-5y+2 与字母x的取值无关 则2-2b=0,3a+6=0 则b=1,a=-2