等比数列(高考题)

1. (2014重庆,2,5分,★★☆)对任意等比数列{an},下列说法一定正确的是( ) A.a1,a3,a9成等比数列 B.a2,a3,a6成等比数列 C.a2,a4,a8成等比数列 D.a3,a6,a9成等比数列

2. (2012安徽,5,5分,★★☆)公比为2的等比数列{an}的各项都是正数,且a3a11=16,则a5=( ) A.1 B.2 C.4 D.8

3. (2013江西,3,5分,★★☆)等比数列x,3x+3,6x+6,…的第四项等于( ) A.-24 B.0 C.12 D.24

4. (2010全国Ⅰ,4,5分,★★☆)已知各项均为正数的等比数列{an},a1a2a3=5,a7a8a9=10,则a4a5a6=( ) A.5

B.7 C.6 D.4

5. (2014江苏,7,5分,★☆☆)在各项均为正数的等比数列{an}中,若a2=1,a8=a6+2a4,则a6的值是________.

6. (2012广东,12,5分,★★☆)若等比数列{an}满足a2a4=,则a1a5=________. 7. (2011广东,11,5分,★★☆)已知{an}是递增等比数列,a2=2,a4-a3=4,则此数列的公比q=________.

8. (2012辽宁,14,5分,★★☆)已知等比数列{an}为递增数列.若a1>0,且2(an+an+2)=5an+1,则数列{an}的公比q=________.

9. (2014河北保定调研,★★☆)在数列{an}中,已知a1=1,an+1=2an+1,则其通项公

1

式为an=( )

A.2n-1 B.2n-1+1 C.2n-1 D.2(n-1)

10. (2011四川,9,5分,★★☆)数列{an}的前n项和为Sn,若a1=1,an+1=3Sn(n≥1),则a6=( )

A.3×44 B.3×44+1 C.45 D.45+1

11. (2013课标全国Ⅰ,14,5分,★★☆)若数列{an}的前n项和Sn=an+,则{an}的通项公式是an=________.

12. (2014天津,5,5分,★☆☆)设{an}是首项为a1,公差为-1的等差数列,Sn为其前n项和.若S1,S2,S4成等比数列,则a1=( ) A.2 B.-2 C. D.-

13. (2014课标Ⅱ,5,5分,★☆☆)等差数列{an}的公差为2,若a2,a4,a8成等比数列,则{an}的前n项和Sn=( ) A.n(n+1) B.n(n-1) C.

D.

14. (2014安徽,12,5分,★☆☆)数列{an}是等差数列,若a1+1,a3+3,a5+5构成公比为q的等比数列,则q=________.

2