等差数列的前n项和为Sn,则S13是几倍的S6?
人气：222 ℃ 时间：2020-01-29 09:28:14
解答
sn=na1+(n-1)nd/2
s6=6a1+15d
s13=13a1+78d
是否存在倍数关系a1和d
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