举报
汐音
(1/2+1/3+1/4+...+1/2007)×(1+1/2+1/3+1/4+...+1/2006)-(1+1/2+1/3+1/4+...+1/2007)×(1/2+1/3+1/4+...+1/2006 )
=(1/2+1/3+1/4+...+1/2006+1/2007)×(1+1/2+1/3+1/4+...+1/2006)-(1+1/2+1/3+1/4+...+1/2006+1/2007)×(1/2+1/3+1/4+...+1/2006 )
=(1/2+1/3+1/4+...+1/2006)×(1+1/2+1/3+1/4+...+1/2006)+1/2007(1+1/2+1/3+1/4+...+1/2006)
-(1+1/2+1/3+1/4+...+1/2006)×(1/2+1/3+1/4+...+1/2006 -1/2007(1+1/2+1/3+1/4+...+1/2006)+1/2007
=1/2007