Question

等差数列问题求助！

已知等差数列{An}满足A1+A2+A3+A101=0，则A1=1，Sn最大值为？

Answer 1

A1+A2+A3+A101=0
A1+A1+d+A1+2d+A1+100d=0
4A1+103d=0
103d=-4A1=-4
d=-4/103
Sn=A1n+n*(n-1)d/2 =n+n(n-1)*(-4/103)/2
=n-(4n^2-4n)/206=(206n-4n^2+4n)/206=(-4n^2+210n)/206 求此最大值就行了,打不下了