设数列{an}的前n项和为Sn,且a1=1,Sn=nan-2n(n-1)(1)求a2,a3,a4,并求出数列{an}的通项公式.(2)设数列{1/an.an 1}的前n项的和为Tn,试求Tn的取值范围.

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设数列{an}的前n项和为Sn,且a1=1,Sn=nan-2n(n-1)(1)求a2,a3,a4,并求出数列{an}的通项公式.(2)设数列{1/an.an 1}的前n项的和为Tn,试求Tn的取值范围.

设数列{an}的前n项和为Sn,且a1=1,Sn=nan-2n(n-1)(1)求a2,a3,a4,并求出数列{an}的通项公式.(2)设数列{1/an.an 1}的前n项的和为Tn,试求Tn的取值范围.
设数列{an}的前n项和为Sn,且a1=1,Sn=nan-2n(n-1)
(1)求a2,a3,a4,并求出数列{an}的通项公式.(2)设数列{1/an.an 1}的前n项的和为Tn,试求Tn的取值范围.

设数列{an}的前n项和为Sn,且a1=1,Sn=nan-2n(n-1)(1)求a2,a3,a4,并求出数列{an}的通项公式.(2)设数列{1/an.an 1}的前n项的和为Tn,试求Tn的取值范围.
1.
Sn=nan-2n(n-1)
S(n-1)=(n-1)a(n-1)-2(n-1)(n-2)
an=Sn-S(n-1)
=nan-(n-1)a(n-1)-4(n-1)
(n-1)an-(n-1)a(n-1)-4(n-1)=0
an-a(n-1)-4=0
an=a1+4(n-1)
=4n-3
a2=5
a3=9
a4=13
2.

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