2a11=a1+a21,2b11=b1+b21
∴ a11/b11
=2a11/2b11
=(a1+a21)/(b1+b21)
=[(a1+a21)*21/2]/[(b1+b21)*21/2]
=A21/B21
=(7*21+1)/(4*21+27)
=148/111
=4/3
若两个等差数列{an},{bn}的前n 项和分别为An和Bn,且满足An/Bn=(7n+1)/(4n+27),则a11/
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