2A+B
=2(-y²+ay-1)+(2y²+3ay-2y-1)
=-2y²+2ay-2+2y²+3ay-2y-1
=(5a-2)y-3
因它的取值与y无关,可得含y的项的系数为0,于是有:
5a-2=0
解得:a=2/5