问题
填空题
设数列{an}为正项等比数列，且an+2=an+1+an，则其公比q=______．
答案
由题设条件知a1+a1q=a1q2，
∵a1＞0，∴q2-q-1=0
解得q=
，∵数列{an}为正项等比数列，1± 5 2
∴q=
．1+ 5 2
故答案：
．1+ 5 2
搜题请搜索小程序“爱下问搜题”
设数列{an}为正项等比数列，且an+2=an+1+an，则其公比q=______．
由题设条件知a1+a1q=a1q2，
∵a1＞0，∴q2-q-1=0
解得q=
，∵数列{an}为正项等比数列，1± 5 2
∴q=
．1+ 5 2
故答案：
．1+ 5 2
Jenny: Sam, you look unhappy. What’s the matter? Sam: My best friend, John is ill in hospital. Jenny: 小题1: What’s wrong with him? Sam: He has a stomachache and can’t eat anything. Jenny: But he looks very healthy, I think. Sam: 小题2: He’s too fat because he eats too much meat. Jenny: 小题3: Sam: You are right. His doctor told him to take more exercise and eat less meat, but he didn’t listen to him. Jenny: 小题4: Sam: Yes. Now he thinks his doctor is right and he begins to do what he told him. Jenny: 小题5: Sam: Me, too.
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