(-2x²)·(3x²-ax-6)-3x(x²+1)
=-6x^4+2ax³+12x²-3x³-3x
=-6x^4+x³(2a-3)+12x²-3x
2a-3=0
a=1.5
不懂可追问,有帮助请采纳,谢谢!