1+2-3-4+5+6-7-8+9+..........+2002-2003-2004+2005
=1+(2-3-4+5)+.............+(2002-2003-2004+2005)
=1+0+.............+0
=1
1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + 9 + 10 - ... + 2002 - 2003 - 2004 + 2005 ( có 2005 số, 2005:4 dư 1)
= 1 + (2 - 3 - 4 + 5) + (6 - 7 - 8 + 9) + ... + (2002 - 2003 - 2004 + 2005)
= 1 + 0 + 0 + ... + 0
= 1
Ủng hộ mk nha ♡_♡