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Smaranda2007
a fost răspuns

Efectuati:

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

Răspuns :

08101971
S = 1+2-3+4+5-6+7+8-9+...+2008+2009-2010+2011
S =  1+2+3+...+2011-3-6-9-...-2010
S = 2011*2012/2 - 3(1+2+...+670)
S = 2011*1006 - 3*670*671/2
S = 2011*1005 + 2011 - 1005*671
S = 1005(2011-671) + 2011
S =  1340*1005+2011 
S = 1348711

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