Tính tổng sau:

2 + (–3) + 4 + (–5) + ...... + 2008 + (–2009) + 2010 + (–2011) + 2012.

2 + (–3) + 4 + (–5) + ... + 2010 + (–2011) + 2012

= 2 + (4 – 3) + (6 – 5) + ... + (2010 – 2009) + (2012 – 2011)

= 2 + 1 + 1 + 1 + ... + 1 (1005 số 1)

= 2 + 1005

= 1007.