Question

S2=1+2-3+4+5-6+7+8-9+...2008+2009-2010+2011

Answer 1

E o formula pentru suma a n termeni
$\frac{n(n+1)}{2}$
Deci
1+2+3+4+.....+2011=$\frac{2011(2011+1)}{2}= \frac{2011*2012}{2}= 2023066$