1、 1 2017 6.2 n 60 an a7 a9 16 S11 99 2 a12 ( ) A 15 B 30 C 31 D 64 A 2a8 a7 a9 16 a8 8 S11 a1 a11 2 a6 2 11a6 99 2 a6 9 2 d a8 a6 2 7 4 a12 a8 4d 15 A. 2 Sn an n n N * an 1 an a2 a3 2 S2014 ( ) A C C an 1 an a2 n 1 a2 a1 a2 a1 0 n 2 a3 2 2a2 a2 1 an 1 an 1 an 0 1 S2014 2 C. 3 an a1 1 a2 1 2 2 an 1 1
2、an 1 an 2 (n N * ) ( ) A an 1 nB an 2 n 1C an 2 n 2D an 3 n A 2 an 1 1 an 1 an 2 1 an 1 1 an 1 an 2 1 an 1 1 an 1 a1 1 1 a2 1 a1 2 1 1 1 an n an 1 n . 4 201 an n Sn S3 9 S6 36 a7 a8 a9 ( ) A 63 B 45 C 36 D 27 B 2 S3 9 S6 S3 36 9 27 S3 S6 S3 S9 S6 S9 S6 45 S9 S6 a7 a8 a9 45 B. 5 an 60 260 Sn 520 a7 (
3、 ) A 20 B 40 C 60 D 80 B 60 260 (60 80.Sn (60 40. 13 a7 a7 40. 6 an n Sn S4 S2 4 S6 S4 ( ) A. 9 4B. 3 2C. 5 3D 4 A S4 S2 4 S2 x S4 4x. S2 S4 S2 S6 S4 2(S4 S2) S2 (S6 S4) S6 3S4 3S2 12x 3x 9x S6 S4 9x 4x 9 4 . 7 an n Sn a1 3 ak 1 3 2 Sk 12 k _. 13 Sk 1 Sk ak 1 12 3 2 21 2 Sk 1 k a1 ak 1 2 k 3 3 2 2 2
4、1 2 k 13. an n Sn an Sn a1 _. 1 4 an d Sn d 2 n 2 (a1 d 2 )n 3 Sn d 2 n 2 a1 d 2 n Sn Sn n ( ) a1 d 2 0 Sn d 2 n Sn d 2 d 2 d d 0( ) d 1 2 a1 1 4 . 9 an n Sn S2 10 S5 55 a10 _. 39 an d a1 a1 d 10 5a1 2 d 55 2a1 d 10 a1 2d 11 a1 3 d 4 a10 a1 (10 1)d 39. 10 an bn a10 b 2 2 b1b3 a 4 (a d) 2 (a d) 2 (a
5、2 d 2 ) 2 a 2 d 2 a 2 a 2 a 2 d 2 ( ) d 2a. d 2a q b2 b1 a2 a1 2 (1 2) 2 3 2 20 n ( ) A 11 B 19 C 20 D 21 B a11 a10 0 a110 S20 a1 a20 2 10(a10 a11)0 n 19. an a5 12 a20 18. (1) an (2) |an| n Sn. 5 (1) an d a5 a1 4d 12 a20 a1 19d 18 a1 20 d 2 an 20 (n 2) 2n 22. (2) (1) |an| | 2n 22| 2n 22 n 2n 22 n11
6、n Sn 20 18 ( 2n 22) n 2n 2 (21 n)n n11 Sn S11 2 4 (2n 22) 110 n 2n 2 n 2 21n 220. Sn n n n n 2 21n 220 n11 . 16 an n Sn 2Sn a 2 n n 4. (1) an (2) an (1) n 1 2a1 a 2 1 1 4 a 2 1 2a1 3 0 a1 3(a1 1 ) n 2Sn 1 a 2 n 1 n 5 2Sn a 2 n n 4 2an a 2 n a 2 n 1 1 a 2 n 2an 1 a 2 n 1 (an 1) 2 a 2 n 1 an 1 an 1 an 1 an 1. an 1 an 1 an an 1 1 a1 3 a2 2 an an 1 an 1 an an 1 1 an (2) (1) a1 3 d 1 an an 3 (n 1) n 2 an n 2.
