若｛an｝首项为a,公差为d,｛bn｝满足：bk=（a1+a2+..+ak)(k属于N*）.问｛bn｝是否为等差数列?说明理由
bk=（a1+a2+..+ak）/k
人气：277 ℃ 时间：2019-09-22 09:56:22
解答
An=a+(n-1)d
Bk=((A1+Ak)×k/2)/k=(A1+A1+(k-1)d)/2=a+(k-1)d/2
Bk-B(k-1)=a+(k-1)d/2-a-(k-2)d/2=d/2
{Bk}是等差数列
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