题目

已知等比数列{an}中,an>0,a1、a99为方程x2－10x+16=0的两个根,则a40·a50·a60等于A.32                                   B.64                             C.256                           D.±64 答案：解析:由等比数列性质知a1·a99=a40·a60=a502=16.又an>0,∴a50=4.∴a40·a50·a60=16×4=64.答案:B

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