Question

若3k,2k+2,3k+3是等比数列的前3项,则第四项为

Answer 1

3k/(2k+2)=(2k+2)/(3k+3)

9k^2 +9k=4k^2 +8k +4

5k^2 +k- 4=0

(5k-4)(k+1)=0

k=4/5 or -1

12/5 ,18/5 ,27/5 所以下一个是81/10

81/10=?(4/5)

81/10=?(8/10)

81/10=10k+1/10