非標準答案，僅供參考

我們知道：
1^2 + 2^2 + ... + 10^2 = 330
方法如下：
10^2 - 5^2 = 75
9^2 - 4^2 = 65
8^2 - 3^2 = 55
7^2 - 2^2 = 45
6^2 - 1^2 = 35
5^2 - 0^2 = 25
上麵是300。the rest is: 4^2 + 3^2 + 2^2 + 1^2, which is 30.
So the total is 330

Similar way for 1^2 + 2^2 + ... + 20^2:

20^2 - 10^2 = 300
19^2 - 9^2 = 280
....
11^2 - 1^2 = 120
10^2 - 0^2 = 100

which is 5 x 400 + 200

So the total is 2200 + 330 - 100 which is 2430.

I guess everyone understands the above calculation. My son taught me this :)

所有跟帖： 

• 這兒子真牛！ -戲雨飛鷹- ♀ (0 bytes) () 07/23/2009 postreply 14:47:33

• sorry，沒說好。I mean LZ的兒子真牛。將來一定會進哈佛/麻省理工。 -戲雨飛鷹- ♀ (0 bytes) () 07/23/2009 postreply 14:52:07

• :)) 天天玩game ... ai -botong- ♂ (0 bytes) () 07/23/2009 postreply 18:42:18

• 好像有問題 -路人_甲- ♂ (63 bytes) () 07/23/2009 postreply 17:55:49

• 甲兄對的,謝謝! -botong- ♂ (0 bytes) () 07/23/2009 postreply 18:44:19

• 回複：甲兄對的,謝謝! -路人_甲- ♂ (50 bytes) () 07/23/2009 postreply 19:54:41

• 過獎 -botong- ♂ (36 bytes) () 07/24/2009 postreply 08:22:33