已知等比数列{an},首项为81,数列{bn}=log3an,其前n项和为Sn、证明{bn}是等差数

证：设等比数列{an}公比为q,对于数列{bn},对数有意义,q>0an=a1×q^(n-1)n=1时,b1=log3(a1)=log3(81)=4n≥2时,bn=log3(an)=log3(a1×q^(n-1))=log3(a1)+log3(q^(n-1))=log3(81)+(n-1)log3(q)=(n-1)log3(q) +4b(n-1)=l...