Question

(2n+1)的阶乘除以(2n-1)阶乘等于?

Answer 1

(2n+1)!=(2n+1)*2n*(2n-1)*(2n-2)...*2*1
(2n-1)!=(2n-1)*(2n-2)*(2n-3)...*2*1
上式除以下式
(2n+1)!/(2n-1)!=(2n+1)*2n=2n(2n+1)