已知数列满足an+1-an=2(n属于N),且a9=17数列{bn}中,bn=3^an,求证数列{bn}是等比数列并...已知数列满足an+1-an=2(n属于N),且a9=17数列{bn}中,bn=3^an,求证数列{bn}是等比数列并求其前n项和sn

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$已知数列满足an+1-an=2(n属于N*),且a9=17数列{bn}中,bn=3^an,求证数列{bn}是等比数列并...已知数列满足an+1-an=2(n属于N*),且a9=17数列{bn}中,bn=3^an,求证数列{bn}是等比数列并求其前n项和sn$

已知数列满足an+1-an=2(n属于N*),且a9=17数列{bn}中,bn=3^an,求证数列{bn}是等比数列并...已知数列满足an+1-an=2(n属于N*),且a9=17数列{bn}中,bn=3^an,求证数列{bn}是等比数列并求其前n项和sn
已知数列满足an+1-an=2(n属于N*),且a9=17数列{bn}中,bn=3^an,求证数列{bn}是等比数列并...
已知数列满足an+1-an=2(n属于N*),且a9=17数列{bn}中,bn=3^an,求证数列{bn}是等比数列并求其前n项和sn

已知数列满足an+1-an=2(n属于N*),且a9=17数列{bn}中,bn=3^an,求证数列{bn}是等比数列并...已知数列满足an+1-an=2(n属于N*),且a9=17数列{bn}中,bn=3^an,求证数列{bn}是等比数列并求其前n项和sn
an+1-an=2,{an}是d=2的等差,
a9=a1+8d=17,所以 a1=1
an=a1+(n-1)d=2n-1
bn=3^an,b(n+1)=3^a(n+1),
b(n+1)/bn=3^[a(n+1)-an]=3^2=9,所以 {bn}是q=9的等比数列.
b1=3,
Sn=b1(1-q^n)/(1-q)=(3/8)(9^n -1)

17=a9=2*8+a1
a1=1
an=2n-1
bn=3^(2n-1)
bn+1:bn=9
sn=3*(9^n-1)/8

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