题目

设a1=2,数列{1+2an}是公比为2的等比数列,则a6等于(    )A.31.5                B.160                C.79.5                D.159.5 答案：C解析：∵a1=2,∴1+2a1=5,1+2an=5×2a-1.解得a6=79.5,故选C.

查看本题答案和解析