2010

來源: 2024-02-15 10:24:22 [舊帖] [給我悄悄話] 本文已被閱讀:

2010/1 - 2009/2 + 2008/3 - 2007/4 + ... - 1/2010
   + 1/1006 + 3/1007 + 5/1008 + ...+ 2009/2010

= 2010/1 + 2009/2 + 2008/3 + 2007/4 + ... + 1/2010
   - 2*2009/2 - 2*2007/4 - ... - 2*1/2010
   + 1/1006 + 3/1007 + 5/1008 + ...+ 2009/2010

= 2010/1 + 2009/2 + 2008/3 + ... + 1/2010
   - 2009/1 - 2007/2 - ... - 1/1005
   + 1/1006 + 3/1007 + 5/1008 + ...+ 2009/2010
 
= 1 + 2/2 + 3/3 + ... + 1005/1005
   + 1005/1006 + 1004/1007 + ... + 1/2010
   + 1/1006 + 3/1007 + 5/1008 + ...+ 2009/2010
   
 = 1 + 2/2 + 3/3 + ... + 1005/1005
   + 1006/1006 + 1007/1007 + ... + 2010/2010

 = 1 + 1 + ... + 1   // 2010 times

 = 2010