作业帮若两个等差数列{an},{bn}的前n项和分别为An,Bn,且满足An\Bn=4n+2/5n-5,则 a13/b13 的值为 A,51/60 B.60/51 C.19/20 D.7/8
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若两个等差数列{an},{bn}的前n项和分别为An,Bn,且满足An\Bn=4n+2/5n-5,则 a13/b13 的值为 A,51/60 B.60/51 C.19/20 D.7/8
若两个等差数列{an},{bn}的前n项和分别为An,Bn,且满足An\Bn=4n+2/5n-5,则 a13/b13 的值为
A,51/60 B.60/51 C.19/20 D.7/8
若两个等差数列{an},{bn}的前n项和分别为An,Bn,且满足An\Bn=4n+2/5n-5,则 a13/b13 的值为 A,51/60 B.60/51 C.19/20 D.7/8
a13/b13=2a13/2b13=(a1+a17)/(b1+b17)={[(a1+a17)x17]/2}/{[b1+b17)x17]/2}=A17/B17=[4x17+2)]/[5x17-5]=7/10
A25/B25=a13/b13=102/120=17/20