题目

已知｛an｝是等比数列，且an＞0，a2a4+2a3a5+a4a6=25,那么a3+a5的值为A.5                              B.10                             C.15                                   D.20 答案：解析:∵a2a4=a32,a4·a6=a52，∴(a3+a5)2=25.又an＞0，∴a3+a5=5.答案:A

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