(2-4-6+8)+(10-12-14+16)+...+(1994-1996-1998+2000)
= (2+8-4-6)+(10+16-12-14)+...+(1994+2000-1996-1998)
= 0+0+....+0
= 0
Đặt: A=2-4-6+8+10-12-...+1994-1996-1998+2000
Ta có: A=2-4-6+8+10-12-...+1994-1996-1998+2000
=> A= (2 – 4 – 6 + 8) + (10- 12 – 14 + 16) + … + (1994 – 1996 – 1998 + 2000)
=> A = 0 + 0 + … + 0
=> A = 0
Vậy 2-4-6+8+10-12-...+1994-1996-1998+2000=0