9. Geometric; a1=3, r=2
11. Not geometric
13. Geometric; a1=1, r=−3
15. Geometric; a1=7, r=−1
17. Geometric; a1=9, r=13
19. Geometric; a1=−12, r=−12
21. Geometric; a1=1, r=2
23. Not geometric
25. Geometric; a1=13, r=13
27. Geometric; a1=5–√, r=5–√
29. a1=2, r=5, an=2(5)n−1
31. a1=5, r=23, an=5 (23)n−1
33. a1=0.2, r=−3, an=0.2(−3)n−1
35. a1=π4, r=π2, an=π2n+2
37. an=3⋅2n
39. an=108⋅(13)n
41. an=−15⋅4n
43. a7=320
45. a10=−1536
47. a6=24316
49. a9=−390, 625256
51. a20=−125131, 072
53. 11
55. 10
57. 9
59. S10=1,220,7035
61. S12=−40, 690, 10425
63. S8=109, 22516, 384
65. 3116
67. 6305729
69. 255
71. 3(520−220)35(2)19
73. 0.397
75. 9841.333
77. 2.250
79. 12
81. −13
83. 325
85. 152
87. 45