※ 引述《Yic0197 (科科科55)》之銘言:
: 要如何從左式子湊成右式子,在做題當下滿難想得到?
: https://i.imgur.com/f6elrcc.jpg
1 * 3 * 5 * ... * (2n - 3)
_________________________
2 * 4 * 6 * ... * 2n
(2n - 2)!
= _____________________________
[2 * 4 * ... * (2n - 2)]^2 * 2n
(2n - 2)!
= _____________________________
2^(2n-2) * [(n - 1)!]^2 * 2 n
(2n - 2)!
= _____________________________
2^(2n-1) * (n - 1)! * n!
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