Tính giá trị biểu thức A = 1 + 2 – 3 – 4 + 5 + 6 – 7 – 8 + … + 2009 + 2010 – 2011 – 2012 + 2013
Giải thích
A = 1 + 2 – 3 – 4 + 5 + 6 – 7 – 8 + … + 2009 + 2010 – 2011 – 2012 + 2013.
= (1 – 3) + (2 – 4) + (5 – 7) + (6 – 8) + … + (2009 – 2011) + (2010 – 2012) + 2013
= (–2) + (–2) + (–2) + (–2) + … + (–2) + (–2) + 2013
= (–2). 1006 + 2013 = 1.
Vậy A = 1.