等差数列Sn=(a1+a1+(n-1)d)n/2=a1n+n(n-1)d/2 没有常数项
所以Sn=n²+2n-1 不是等差数列
选C
数列判断
数列判断
数列｛an}的前n项和为Sn=n*n+2*n-1 则这个数列一定是（）
A 等差数列
B常数列
C非等差数列
D等差数列或常数列
数列｛an}的前n项和为Sn=n*n+2*n-1 则这个数列一定是（）
A 等差数列
B常数列
C非等差数列
D等差数列或常数列
数学人气：760 ℃时间：2020-04-02 04:41:41
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