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问题: 小数列题`

等差数列,a1=1 S2n/Sn=(4n+2)/(n+1)


an=

解答:

显然S2n/Sn=(4n+2)/(n+1)对n=1肯定成立
S2/S1 =(4+2)/(1+1)=3
S1=a1=1==> S2=3 ==>a2=2
等差数列,a1=1,a2=2 ===>an=n