等差数列{an},{bn}的前n项和分别为An,Bn,且A
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等差数列{an},{bn}的前n项和分别为An,Bn,且
A
∵数列{an},{bn}均为等差数列,且其前n项和分别为An,Bn,
∴ a5 b5= a1+a9 2 b1+b9 2= (a1+a9)•9 2 (b1+b9)•9 2= A9 B9. ∵ An Bn= 7n+45 n+3, ∴ a5 b5= A9 B9= 7×9+45 9+3=9. 故答案为:9.
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