[原創]升到中4，好多數唔識計，不斷更新問題，更新左 [複製鏈接]

引用第36樓yhmjack1於2010-10-01 20:25發表的  :
Let p(n) be the statement
n^3+5n is divisble by 6
For n=1
(1)^3+5(1)
=1+5
.......

點解紅色果度係咁ge??
why 3k^2+3k = 6N??點解ge

引用第40樓scfkipper於2010-10-01 22:31發表的  :
點解紅色果度係咁ge??
why 3k^2+3k = 6N??點解ge

你大可以用MI prove佢
這些題目要細心考慮.....
這些= 1+2+3+....+n=(n(n+1))/2
當係well-known knowlegde

引用第40樓scfkipper於2010-10-01 22:31發表的  :
點解紅色果度係咁ge??
why 3k^2+3k = 6N??點解ge

you may consider 3k² + 3k = 3k(k+1) , hence either k or k+1 is even ( 2 consecutive integers)
 => 3k(k+1) is divisible by 2 & 3 => divisible by 6