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b) 11 +12 +13 +......+78 ( suma Gauss)

Răspuns :

11 + 12 + 13 + .... + 78 = 3 026

→ stabilesc cati termeni are suma cu ratia = 1

78 - 11 + 1 = 67+ 1 = 68 termeni are suma

→ aplic formula sumei lui Gauss

= 68 × ( 11 + 78 ) : 2 =

= 34 × 89 =

= 3 026