Question

解答初一的几道数学题要过程

1-2+3-4+5-6+·····+99-100

把18-（-13）+（-21）-（-42）写成省略括号的和是：

计算：见图

Answer 1

(1+3+5+...+97+99)-(2+4+...+98+100)
=(1+99)*50/2-(2+100)*50/2
=-50

18-（-13）+（-21）-（-42）
=18+13-21+42
=52

1/1x2+1/2x3+```````+1/2008x2009
=1-1/2+1/2-1/3+1/3-1/4+````````+1/2008-1/2009
=1-1/2009
=2008/2009

Answer 2

1-2+3-4+5-6+·····+99-100
=(1-2)+(3-4) 一共有50组，每组值为－1所以
=-1x50
=-50

18-（-13）+（-21）-（-42）
=18+13-21+42
=52

1/1x2+1/2x3+```````+1/2008x2009
=1-1/2+1/2-1/3+1/3-1/4+````````+1/2008-1/2009
=1-1/2009
=2008/2009

Answer 3

1-2+3-4+5-6+·····+99-100
=-1*50=-50
18-（-13）+（-21）-（-42）
=18+13-21+42

=1-1/1+1/2-1/3+1/3-......+1/2008-1/2009
=1-1/2009
=2008/2009