两个等差数列{an}{bn},a1=0,b1=-4,Sk,Sk’分别是这两个数列前k,项和,若Sk+Sk’=0,则ak+bk=?
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![两个等差数列{an}{bn},a1=0,b1=-4,Sk,Sk’分别是这两个数列前k,项和,若Sk+Sk’=0,则ak+bk=?](/uploads/image/z/14575177-1-7.jpg?t=%E4%B8%A4%E4%B8%AA%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%7Ban%7D%7Bbn%7D%2Ca1%3D0%2Cb1%3D-4%2CSk%2CSk%E2%80%99%E5%88%86%E5%88%AB%E6%98%AF%E8%BF%99%E4%B8%A4%E4%B8%AA%E6%95%B0%E5%88%97%E5%89%8Dk%2C%E9%A1%B9%E5%92%8C%2C%E8%8B%A5Sk%2BSk%E2%80%99%3D0%2C%E5%88%99ak%2Bbk%3D%3F)
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两个等差数列{an}{bn},a1=0,b1=-4,Sk,Sk’分别是这两个数列前k,项和,若Sk+Sk’=0,则ak+bk=?
两个等差数列{an}{bn},a1=0,b1=-4,Sk,Sk’分别是这两个数列前k,项和,若Sk+Sk’=0,则ak+bk=?
两个等差数列{an}{bn},a1=0,b1=-4,Sk,Sk’分别是这两个数列前k,项和,若Sk+Sk’=0,则ak+bk=?
Sk=(0+ak)k/2
Sk’=(-4+bk)k/2
Sk+Sk’=0=k/2(ak+bk-4)
所以ak+bk-4=0
所以ak+bk=4
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Sk+Sk'=0
(a1+ak)*k/2+(b1+bk)*k/2=0
k/2≠0
所以a1+ak+b1+bk=0
a1=0,b1=-4
所以ak+bk=4
Sk+Sk'=(a1+ak)*k/2+(b1+bk)*k/2=[(a1+b1)+(ak+bk)]*k/2…k不等于0,所以ak+bk=-(a1+b1)……手机打的,没注意题上的原始数据,不敢乱带数据……给个分吧,谢谢
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