S1/T1=(3+1)/4=1,
即S1=T1,
得a1=b1令an公比为q,
bn公比为pS2/T2=(a1+a1q)/(a1+a1p)=(1+q)/(1+p)=(3²+1)/4=5/2,得:2+2q=5+5p,
即q=(3+5p)/2S3/T3=(3³+1)/4=7=(1+q+q²)/(1+p+p²)代入q,化简得:7+7p+7p²=1+(3+5p)/2+(3+5p)²/4p²-4p+3=0得p=1,
3,从而q=4,
9p=1时,Sn=n,
Tn=a1(4^n-1)/3,
不符合Sn/Tn的等式,舍去。p=3时,q=9,
Sn/Tn符合题意。所以a3/b3=q²/p²=81/9=9