(1)
3(Sn)^2=An(3Sn-1),
n≥2,An=Sn-S(n-1),
所以
3(Sn)^2=[Sn-S(n-1)](3Sn-1)
=3(Sn)^2-Sn-3SnS(n-1)+S(n-1)
3SnS(n-1)+Sn-S(n-1)=0,
SnS(n-1)≠0,两边同除以SnS(n-1)
1/Sn-1/S(n-1)=3,
1/S1=1/a1=1,
所以{1/Sn}是以1为首项,公差为3的等差数列.
(2)
由(1)知
1/Sn=1+3(n-1)=3n-2,
所以Sn=1/(3n-2),
Bn=Sn/(3n+1)
=1/[(3n+1)(3n-2)]
=1/3[1/(3n-2)-1/(3n+1)]
所以
Tn=B1+B2+...+Bn
=1/3[1-1/4+1/4-1/7+...-1/(3n-2)+1/(3n-2)-1/(3n+1)]
=1/3[1-1/(3n+1)]
=n/(3n+1)