→ Desperato : 3. a=1, b=n^2 ? 02/24 22:54
→ freePrester : k*k! = (k+1)! - k! 02/24 22:56
推 tommyxu3 : b不是從1加到n^2嗎? 02/24 23:01
推 tyz : 1. 第n項為3/n(n+1)(n+2) 02/25 00:23
→ tyz : 可拆為(3/2)[1/n(n+1)-1/(n+1)(n+2)] 02/25 00:24
→ tyz : 兩兩互消後整理為(3n^2+9n)/4(n+1)(n+2) 02/25 00:26