等差数列{An},{bn}的前n项和为An,Bn,且An/Bn=n/3n-2,则a5/b5=?
人气:266 ℃ 时间:2020-03-24 08:30:53
解答
因为a1+a9=2*a5
A9=9(a1+a9)/2=9*2*a5/2=9*a5 a5=A9/9
同理有B9=9*b5 b5=B9/9
a5/b5=(A9/9)/(B9/9)=A9/B9=9/25
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