(an+1)/(an-1)=((a(n-1)+1)/(a(n-1)-1))^2
bn/b(n-1)=(log(9)(a(n-1)+1)/(a(n-1)-1))/log(9)((an+1)/(an-1))=log((an+1)/(an-1)) (a(n-1)+1)/(a(n-1)-1)=1/2
(an+1)/(an-1)=((a(n-1)+1)/(a(n-1)-1))^2
bn/b(n-1)=(log(9)(a(n-1)+1)/(a(n-1)-1))/log(9)((an+1)/(an-1))=log((an+1)/(an-1)) (a(n-1)+1)/(a(n-1)-1)=1/2