高二的已知两个等差数列{an}和{bn}的前n项和sn和tn,且sn/tn=7n+1/4n+27,则a11/b11=?
高二的已知两个等差数列{an}和{bn}的前n项和sn和tn,且sn/tn=7n+1/4n+27,则a11/b11=?
数学人气:878 ℃时间:2020-04-06 13:52:03
优质解答
4/3 S21=(a1+a21)*21/2 a1+a21=a1+a1+20d=2(a1+10d)=2a11 所以S21=2a11*21/2=21*a11 同理T21=21*b11 所以a11/b11=S21/T21 =(7*21+1)/(4*21+27) =4/3
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