2、则的值为()A. B. C. D.【答案】B6.等差数列中,若,则=()A.15B.30C.45D.60【答案】A7.数列是首项的等比数列,且,,成等差数列,则其公比为()A.B.C.或D.【答案】C8.等差数列的前n项和为,且=6,=4,则公差d等于()A.1B.C.-2D.3【答案】C9.已知是等比数列,,则公比=()A.B.C.2D.【答案】D10.某林场计划第一年造林亩,以后每年比前一年多造林,则第三年造林()A.亩B.亩C.亩D.亩【答案】A11.数列是公差不为0的等差数列,且为等比数列的连续三项,则数列的公比为()A.B.4