1-3+5-7+.......+2009-2011
=-2*(2011+1)/4
=-2*503
=-1006
-1006
-1004
总共有(2011+1)/2=1006 个数,你两个两个算,1-3=-2,5-7=-2 所以有503个-2,所以答案是-1006
正数1+5+9+...+2009为首项为a1=1,公差为d1=4的等差数列,n=503个数,s1=503*(1+2009)/2
负数-3-7-11...-2011为首项为b1=-3,公差为d2=-4的等差数列,n=503个数,s2=-503*(3+2011)/2
s1+s2=-1006