(1-1/2²)×(1-1/3²)×···×(1-1/9²)×(1-1/10²)

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(1-1/2²)×(1-1/3²)×···×(1-1/9²)×(1-1/10²)(1-1/2²)×(1-1/3²)×···×(1-1/9&s

(1-1/2²)×(1-1/3²)×···×(1-1/9²)×(1-1/10²)
(1-1/2²)×(1-1/3²)×···×(1-1/9²)×(1-1/10²)

(1-1/2²)×(1-1/3²)×···×(1-1/9²)×(1-1/10²)
1-1/n^2=(n^2-1)/n^2=(n-1)(n+1)/n^2=(n-1)/n * (n+1)/n
如:(1-1/2²)=1/2 * 3/2
(1-1/3²)=2/3 * 4/3
(1-1/9²)=8/9 *10/9
(1-1/10²)=9/10 * 11/10
可知中间项都消去了,只剩了1/2 与 11/10
所以结果为11/20