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Calculați : 1 + 3 + ... + 2009

Răspuns :

1 + 3 + 5 + 7 +...+ 2009 =
Aflam cati termeni are suma:
(2009 - 1) : 2 + 1 = 2008:2+1 = 1005

= (1+2009)×1005 : 2 =

= 2010 × 1005 : 2 =

= 1005 × 1005 =

= 1005^2