题目

已知等差数列{an}的公差为2,若a1,a3,a4成等比数列,则a2等于A.－4                           B.－6                           C.－8                           D.－10 答案：解析:∵a1,a3,a4成等比数列,∴a32=a1·a4.∴(a2+2)2=(a2－2)(a2+4).∴a2=－6.答案:B

查看本题答案和解析