✔ 最佳答案
Please read:
圖片參考:
http://imgcld.yimg.com/8/n/HA00430218/o/20131029222144.jpg
2013-10-30 14:53:15 補充:
當然,你那是用了新公式:
[A] 4*(1/6)(n)(n+1)(2n+1) = (1/6)(2n)(2n+1)(2n+2)
[B] (1/6)(2n)(2n+1)(4n+1) - 2(1/6)(2n)(2n+1)(2n+2)
= (1/6)(2n)(2n+1)[(4n+1) - 2(2n+2)]
= (1/6)(2n)(2n+1)(-3)
= -n(2n+1)
= -(m/2)(m+1) where m = 2n
= -m(m+1)/2
在於教學角度是很好的~
但於答題角度,如題目要求「由此」、「Hence」、「Using the result」,那就不應貿然引入新公式
2013-10-30 14:53:32 補充:
謝謝 那些年 提供的意見~ ^__^