1+(-2)+3+(-4)+5+(-6)+.+2007+(-2008)+2009的和是?
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![1+(-2)+3+(-4)+5+(-6)+.+2007+(-2008)+2009的和是?](/uploads/image/z/1026037-37-7.jpg?t=1%2B%EF%BC%88-2%EF%BC%89%2B3%2B%EF%BC%88-4%29%2B5%2B%28-6%29%2B.%2B2007%2B%28-2008%29%2B2009%E7%9A%84%E5%92%8C%E6%98%AF%3F)
1+(-2)+3+(-4)+5+(-6)+.+2007+(-2008)+2009的和是?
1+(-2)+3+(-4)+5+(-6)+.+2007+(-2008)+2009的和是?
1+(-2)+3+(-4)+5+(-6)+.+2007+(-2008)+2009的和是?
1005
每相邻两项结合
=-1-1-1……-1+2009(共2008/2个-1)
=-1004+2009
=1005
1004+1004*1003-(1004*2+1004*1003)=-1004