(1)原式=1/2000-1/2001+1/1999-1/2000-(1/1999-1/2001)
=1/2000-1/2001+1/1999-1/2000-1/1999+1/2001
=0
(2)原式=(1-1/2)+(1/2-1/4)+(1/4-1/8)……+(1/512-1/1024)
=1-1/1024
=1023/1024
(3)原式=(1+1999)*1999/2=1999000
(1)原式=1/2000-1/2001+1/1999-1/2000-(1/1999-1/2001)
=1/2000-1/2001+1/1999-1/2000-1/1999+1/2001
=0
(2)原式=(1-1/2)+(1/2-1/4)+(1/4-1/8)……+(1/512-1/1024)
=1-1/1024
=1023/1024
(3)原式=(1+1999)*1999/2=1999000