n=1时,an=S1=102n>1时,an=Sn-S(n-1) =-3n²/2+205n/2-[-3(n-1)²/2+205(n-1)/2] =-3n+104祝你开心!希望能帮到你,如果不懂,请追问,祝学习进步!O(∩_∩)O...