-1+3-5+7-9+11…-2005+2007-2009+2011
1个回答

-1+3-5+7-9+11…-2005+2007-2009+2011

=(3-1)+(7-5)+(11-9)+.(2011-2009)

=2×(2011+1)÷4

=2×503

=1006