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Afla suma 11+22+33+44+...+440

Răspuns :

11+22+33+44+...+440 =
dam factor comun pe 11
= 11 × (1 + 2 + 3 + 4 +...+ 40) =

= 11 × 40 × (40 + 1) : 2 =

= 11 × 20 × 41 =

= 220 × 41 =

= 9020