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Efectuati:
1+2-3+4+5-6+7+8-9+8-9+...+2009+2010+2011-2012.


Răspuns :

Suma  lui Gauss: [n×(n+1)/2
(1+2-3+4+5-6+7+8-9+8-9+...+2009+2010+2011)-2012=
2011
×2012/2 - 2012=
=2023066-2012=
=2021054