又a2a3=45,所以a2,a3是方程x2-14x+45=0的两实根,公差d>0,
∴a2<a3∴a2=5,a3=9
∴
|
|
所以an=4n-3
(2)由(1)知sn=2n2-n,
所以bn=
| sn |
| n+c |
| 2n2−n |
| n+c |
∴b1=
| 1 |
| 1+c |
| 6 |
| 2+c |
| 15 |
| 3+c |
又{bn}也是等差数列,∴b1+b3=2b2
即 2•
| 6 |
| 2+c |
| 1 |
| 1+c |
| 15 |
| 3+c |
| 1 |
| 2 |
∴bn=2n是等差数列,故c=−
| 1 |
| 2 |
| sn |
| n+c |
|
|
| sn |
| n+c |
| 2n2−n |
| n+c |
| 1 |
| 1+c |
| 6 |
| 2+c |
| 15 |
| 3+c |
| 6 |
| 2+c |
| 1 |
| 1+c |
| 15 |
| 3+c |
| 1 |
| 2 |
| 1 |
| 2 |