(1)1+2+3+...+2010;
(2)1+(-2)+3+(-4)+...+2009+(-2010);
(1)1+2+3+...+2010;
(2)1+(-2)+3+(-4)+...+2009+(-2010);
1+2+3+…+2010 1+(-2)+3+(-4)+…+2009+(-2010)
=(1+2010)×2010÷2 =[1+(-2)]+[3+(-4)]+…+[2009+(-2010)]
=2021055 =(-1)+(-1)+…(-1)
=(-1)×(2010÷2)
= -1005 就这样