已知数列{an}满足1/a1a2+1/a3a4+……+1/an-1an-2=n-1/a1an,求证{an}等差数列

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已知数列{an}满足1/a1a2+1/a3a4+……+1/an-1an-2=n-1/a1an,求证{an}等差数列
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已知数列{an}满足1/a1a2+1/a3a4+……+1/an-1an-2=n-1/a1an,求证{an}等差数列
已知数列{an}满足1/a1a2+1/a3a4+……+1/an-1an-2=n-1/a1an,求证{an}等差数列

已知数列{an}满足1/a1a2+1/a3a4+……+1/an-1an-2=n-1/a1an,求证{an}等差数列
n=3时
1/a1a2 + 1/a2a3= 2/a1a3
两边乘以 a1a2a3
得到 a3+a1=2a2 前三项满足等差数列
当n>=3时
1/a1a2+1/a2a3+……1/an-1an=(n-1)/a1an ①
1/a1a2+1/a2a3+……1/an-2an-1=(n-2)/a1an-1 ②
①-②--->(n-1)/a1an-(n-2)/a1an-1 = 1/an an-1
两边同时乘以 a1anan-1
得到:(n-1)an-1 - (n-2)an=a1 ③
同理 取n-1时
(n-2)an-2 - (n-3)an-1 =a1 ④
③-④---> (n-1)an-1 - (n-2)an = (n-2)an-2 - (n-3)an-1
(n-1+n-3)an-1 = (n-2)an +(n-2)an-2
2(n-2)an-1=(n-2)an+(n-2)an-2
n>=3
所以 2an-1 = an +an-2 符合等差数列定义
得证

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