题目

设{an}是公差为正数的等差数列,若a1+a2+a3=15,a1a2a3=80,则a11+a12+a13等于(    )A.120                 B.105              C.90                  D.75 答案：解析：设数列{an}的公差为d,由已知得解得d=3或-3(舍).于是a11+a12+a13=a1+a2+a3+30d=105.故选B.答案:B

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