當(dāng)n≥2時(shí),an=Sn-Sn-1=(2an-1)-(2an-1-1)=2an-2an-1,
即
an |
an?1 |
∴數(shù)列{an}是以a1=1為首項(xiàng),2為公比的等比數(shù)列,
∴an=2n?1,Sn=2n?1…(5分)
設(shè){bn}的公差為d,b1=a1=1,b4=1+3d=7,∴d=2
∴bn=1+(n-1)×2=2n-1…(8分)
(2)cn=
1 |
bnbn+1 |
1 |
(2n?1)(2n+1) |
1 |
2 |
1 |
2n?1 |
1 |
2n+1 |
∴Tn=
1 |
2 |
1 |
3 |
1 |
3 |
1 |
5 |
1 |
2n?1 |
1 |
2n+1 |
1 |
2 |
1 |
2n+1 |
n |
2n+1 |
由Tn>
1001 |
2012 |
n |
2n+1 |
1001 |
2012 |
∴Tn>
1001 |
2012 |