已知数列{an}满足an-1 -2an +an+1=0 且a1=2 a3=4 数列{bn}的前n项和为Sn=2bn-1
来源:学生作业帮助网 编辑:作业帮 时间:2024/11/15 08:30:24
已知数列{an}满足an-1 -2an +an+1=0 且a1=2 a3=4 数列{bn}的前n项和为Sn=2bn-1
已知数列{an}满足an-1 -2an +an+1=0 且a1=2 a3=4 数列{bn}的前n项和为Sn=2bn-1
已知数列{an}满足an-1 -2an +an+1=0 且a1=2 a3=4 数列{bn}的前n项和为Sn=2bn-1
(1)
a(n-1) -2an +a(n+1)=0
a(n+1)-an = an - a(n-1)
=a3-a2 (1)
a(n+1)- an = a2 - a1 (2)
(1)+(2)
2[ a(n+1) -an ] = a3 +a1
=6
an -a(n-1) =3
an - a1 = 3(n-1)
an = 3n-1
Sn = 2bn-1
n=1 ,b1=1
for n>=2
bn = Sn -S(n-1)
=2bn - 2b(n-1)
bn =2b(n-1)
=2^(n-1) .b1
=2^(n-1)
(2)
cn =[log(an -1) ]
=[log(3n)]
c1= [log3] =1
c2= [log6] =2
T2 = c1+c2 =1+2 = 3
已知数列{an}满足an+1=2an+3.5^n,a1=6.求an
已知数列an满足 a1=1/2,an+1=3an/an+3求证1/an为等差数列已知数列an满足 a1=1/2,an+1=3an/an+3求证1/an为等差数列
已知数列an满足a1=1,1/an+1=根号1/an^2+2,an>0,求an
已知数列{an}满足a1=1,a2=3,an+2=3an+1-2an求an
已知数列{an}满足a1=1,an+1 -an+2an+1•an=0求通项
已知数列{an}满足a1=2,an+1=2an/an+2,则an等于多少
已知数列{an}满足a1=2,an+1-an=an+1*an,那么a31等于
已知数列{an}满足a1=1 an+1=an/(3an+1) 则球an
已知数列{An}满足A1=1,An+1=2An+2^n.求证数列An/2是等差数列
已知数列{an}满足a1=1/2,an+1=3an+1,求数列{an}通项公式
已知数列an满足an=1+2+...+n,且1/a1+1/a2+...+1/an
已知数列满足a1=1 ,an+1+2an=2 求an
已知数列an满足条件a1=-2 an+1=2an+1则a5
已知数列{an}满足a1=1,an+1=2an+1 1)求证:数列{an+1}为等比数列; 2) 求{an}的通项an
已知数列{an}满足a1=1,an+1·an=2^n 则s2012
已知数列{an}满足An+1=2^nAn,且A1=1,则通项an
已知数列{an}满足a1=1/2,sn=n^2an,求通项an
已知数列an满足a1=1/2,(an+1-1)(an-1)-an+1+an=0求数列an的通项公式