将括号去掉,中间的加法和减法可以抵掉,就剩下1减去二千分之一了,所以是2000分之1999
该试
=1-1/2+1/2-1/3+1/茄竖3-1/4+……+指亩1/1999-1/2000
=1+0+0+…颤逗大…-1/2000
=1999/2000
(1-1/2)+(1/2-1/3)+雀仔(1/3-1/4)+……+(1/1999-1/2000)
=1-1/2+1/岩岁岩2-1/3+1/3-1/4......-1/1999+1/1999-1/粗御2000
=1-1/2000
=1999/2000
1-1/2000=1999/2000 中间都抵消了
(1-1/2)+(岩岁岩1/2-1/3)+粗御(1/3-1/4)+……+(1/1999-1/2000)
=1+(-1/2+1/2)+(-1/3+1/3)+(-1/4+1/4)+……+(-1/1999+1/1999)-1/2000)雀仔
=1-1/2000
=1999/2000