1-2+3-4+...+2007=(1+3+5+7+...2005+2007)-(2+4+6+8+...2006)=2007-1003=1004
首项加末项乘以项数 除以2
(1-2)+(3-4)+(5-6)+.......+(2005-2006)+2007
=(-1)*1003+2007
=1004
(1-2)+(3-4)+(5-6)+.......+(2005-2006)+2007
=(-1)*1003+2007
=1004
1-2+3-4+5-6+.......+2005-2006+2007
=(1-2)+(3-4)+(5-6)+.......+(2005-2006)+2007
=-1-1-1-1-1……-1+2007
=-(2006/2)+2007
=1004