看不懂啊
是Sn=2n^2-(3n+1)
还是Sn=(2n)^2-(3n+1)?
题目容易
令n=1 求出a1=-2
Sn-1=2(n-1)^2-3(3(n-1)+1)
an=Sn-Sn-1=2(2n-1)-3=4n-5