Răspuns :
11+22+33+....+198 =
dam factor comun pe 11
= 11 × (1 + 2 + 3 +...+ 18) =
= 11 × 18 × (18 + 1) : 2 =
= 11 × 9 × 19 =
= 99 × 19 =
= 1 881
dam factor comun pe 11
= 11 × (1 + 2 + 3 +...+ 18) =
= 11 × 18 × (18 + 1) : 2 =
= 11 × 9 × 19 =
= 99 × 19 =
= 1 881