等差数列an中,a1=1前n项和Sn,满足条件S2n/Sn=4n+2/n+1,求an通项
问题描述:
等差数列an中,a1=1前n项和Sn,满足条件S2n/Sn=4n+2/n+1,求an通项
答
额- -
算出等差。。s2/s1=6/2=3
a2+a1=3a1
a2=2a1=2
an=n
答
S2n/Sn=(4n+2)/(n+1),即
S2/S1=6/2
S2=3S1=3a1=3
a2=S2-a1=3-2=1
d=2-1=1
an=n