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Calculati :
-1+2+(-3) +...+ (-2011)


Răspuns :

1+3+5+7...+2011. Termeni (2011-1)/2. +1 = 1006 Suma ((2011 +1)/2 )*1006 = 1006 *1006 2+4+6...+2010 termeni (2010-2)/2 + 1 = 1005 Suma ((2010+2)/2)*1005 =1006*1005 Deci 1006*1006 - prima suma, adica 1006*1005 Rezulta, factor comun 1006(1006-1005), deci 1006