希望大神解答,谢谢.

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希望大神解答,谢谢.
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希望大神解答,谢谢.
希望大神解答,谢谢.

 

希望大神解答,谢谢.
(1)3/4
(2)2/3
(3)5/8
(1-1/2²)(1-1/3²)(1-1/4²)...(1-1/9²)(1-1/10²)...(1-1/n²)
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)(1-1/4)(1+1/4).(1-1/n)(1+1/n)
=1/2×3/2×2/3×4/3×3/4×5/4×...×(n-1)/n·(n+1)/n
=1/2×(n+1)/n
=(n+1)/2n