等差数列{an} {bn}前n项和为An Bn,An/Bn=(7n+2)/(4n+27),求an/bn

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等差数列{an} {bn}前n项和为An Bn,An/Bn=(7n+2)/(4n+27),求an/bn
等差数列{an} {bn}前n项和为An Bn,An/Bn=(7n+2)/(4n+27),求an/bn

等差数列{an} {bn}前n项和为An Bn,An/Bn=(7n+2)/(4n+27),求an/bn
因为等差数列{an} {bn}前n项和为An,Bn
所以an/bn=A2n-1/B2n-1
又An/Bn=(7n+2)/(4n+27)
所以A2n-1/B2n-1=[7*(2n-1)+2]/[4* (2n-1)+27]
所以an/bn=(14n-5)/(8n+23)

An=na1+{n(n-1)Da}/2 Bn=nb1++{n(n-1)Db}/2
An/Bn={2a1+(n-1)Da}/{2b1+(n-1)Db}=(7n+2)K/(4n+27)K （上下同时乘以K）
2a1+(n-1)Da=7nK+2K 所以 2a1-Da=2K nDa=7nK Da=7K a1=4.5K ...

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An=na1+{n(n-1)Da}/2 Bn=nb1++{n(n-1)Db}/2
An/Bn={2a1+(n-1)Da}/{2b1+(n-1)Db}=(7n+2)K/(4n+27)K （上下同时乘以K）
2a1+(n-1)Da=7nK+2K 所以 2a1-Da=2K nDa=7nK Da=7K a1=4.5K
2b1+(n-1)Db=4nK+27K 所以2b1-Db=27K nDb=4nK Db=4K b1=15.5K
an/bn=(7n-2.5)/(4n+11.5)
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