Question

1-2+3-4+5-6+...-2002+2003-2004+2005-2006+2007=?

Answer 1

1-2+3-4+5-6+...-2002+2003-2004+2005-2才2003-2004）+（2005-2006）=-1-1-1-1.-1=-1003

-1003++2007=1004