當(dāng)n≥2時(shí),an=Sn-Sn-1=(2?
1 |
2n?1 |
1 |
2n?2 |
1 |
2n?1 |
經(jīng)驗(yàn)證當(dāng)n=1時(shí),此式也成立,所以an=
1 |
2n?1 |
a1 |
a2 |
又因?yàn)閧bn}為等差數(shù)列,所以公差d=2,∴bn=1+(n-1)?2=2n-1,
故數(shù)列{an}和{bn}通項(xiàng)公式分別為:an=
1 |
2n?1 |
(Ⅱ)由(Ⅰ)可知cn=
2n?1 | ||
|
所以Tn=1×20+3×21+5×22+…+(2n-1)?2n-1 ①
①×2得2Tn=1×21+3×22+5×23+…+(2n-3)?2n-1+(2n-1)?2n ②
①-②得:?Tn=1+2(2+22+…+2n?1)-(2n-1)?2n
=1+2
2(1?2n?1) |
1?2 |
∴數(shù)列{cn}的前n項(xiàng)和Tn=3+(2n?3)?2n.