求等差数列前N项和的公式是什么
求等差数列前N项和的公式是什么
知道首项公差和n
知道首项公差和n
数学人气：621 ℃时间：2020-03-10 04:44:10
优质解答
Sn=na1+n(n-1)d/2
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