在等差数列an中,若am,an,ak成等差数列(公差d≠0).证明:m,n,k也成等差数列
人气：166 ℃ 时间：2020-04-01 12:29:11
解答
m+k = 2n
则
am = a1 + (m-1)d
an = a1 + (n-1)d
ak = a1 + (k-1)d
am+ak = 2a1 + (m+k-2)d = 2a1+2(n-1)d = 2an
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