a1=2/3,an=-2/3,n=14.求等差数列{an}的Sn
已知等差数列{an}满足a1=3,a3=-1.(1)求{an}的通项an;(2)求{an}前n项和Sn的最大值
已知等差数列{an}中,a1=3,前n项和Sn=1/2(n+1)(an+1)-1,求数列{an}的公差.
在等差数列an中,已知a1=3/2,d=-1/2,Sn=-15,求n和an.
1.已知数列{an}是等差数列,a1=2,a1+a2+a3=12,令bn=3^an,求数列{bn}的前n项和Sn.
已知等差数列{an}的前N项和为Sn,a1=-2/3,满足Sn+1/Sn+2=an(n大于等于2)
已知等差数列{an}的前N项和为Sn,a1=-2/3,满足Sn+1/Sn+2=an(n大于等于2),
等差数列{an}中,a1+a2+a3=21,an-2+an-1+an=57,Sn=520,求n.
已知等差数列an满足an+an+1=n+1/2 (1)求an的通项公式 (2)求an的前n项和Sn(3) 求a1,am,
等差数列{an}前n项和为Sn=3n-2n^2,求an
已知等差数列{an}的前N项和为Sn,a1=-2/3,满足Sn+1/Sn+2=an(n大于等于2) 求Sn 别用数学归纳
已知数列{an}a1=2前n项和为Sn 且满足Sn Sn-1=3an 求数列{an}的通项公式an
a1=1/2,an+1=an/an+2,求n/an的sn