Question

-1+2-3+4...-99+100

1/1×2+1/2×3+1/3×4+...+1/2009×2010+1/2010×2011

Answer 1

-1+2-3+4...-99+100
=(-1+2)+(-3+4)+....+(-99+100)
=-1×（100/2)
=-50

追问

还有一个呢1/1×2+1/2×3+1/3×4+...+1/2009×2010+1/2010×2011

追答

1/1×2+1/2×3+1/3×4+...+1/2009×2010+1/2010×2011
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+...+(1/2009-1/2010)+(1/2010-1/2011)
=1-1/2+1/2-1/3+1/3-1/4+...+1/2009-1/2010+1/2010-1/2011
=1+(-1/2+1/2)+(-1/3+1/3)+(-1/4+1/4)...(-1/2010+1/2010)-1/2011
=1-1/2011
=2010/2011

Answer 2

-1+2+-3+4...-99+100=(-1+2)+(-3+4)+...+-99+100=1乘（100/2）=50

Answer 3

只要50乘于51就可以了

追问

什么！！