c) 1 – 2 + 3 – 4 + 5 – 6 + … + 2009 – 2010 + 2011
= 1 + ( -2 + 3 ) + ( -4 + 5 ) + … + ( -2010 + 2011 )
= 1 + 1 + 1+ … + 1 ( 1006 số hạng ) = 1006
tính các dãy số sau:
-1-2+3+4-5-6+7+8-.....-2009-2010+2011
-1-2+3-4-5+6+....-2009+2010-2011
1 – 2 + 3 – 4 + 5 – 6 + … + 2009 – 2010 + 2011
1-2+3-4+5-6+..+2009-2010+2011
Cho A = 1/2001+2/2009+3/2008+........2009/+ 2010/1, B = 1+1/2+1/3+1/4+1/5+1/6+.......1/2010+1/2011. Tính A/B
1- 2- 3+ 4+ 5- 6- 7+ ...+ 2009- 2010- 2011- 2012
1-2-3+4+5-6-7+...+2008+2009-2010-2011
S = 1 - 2 -3 + 4 + 5 -6 - 7 + 8 +....................+ 2009 - 2010 - 2011 + 2012
Tính 1 – 2 + 3 – 4 + 5 – 6 + … + 2009 – 2010 + 2011
Tính B=1-2-3+4+5-6-7+8+......+2009-2010-2011+2012
