Sn/Tn=(2n+2)/(n+3)
(a2+a20)/(b7+b15)
=2a11/2b11
=a11/b11
=11a11/11b11
=S21/T21
=(2*21+2)/(21+3)=11/6
两个等差数列an,bn,其前n项和分别为Sn,Tn,且sn/tn=2n+2/n+3,则a2+a20/b7+b15=?
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