Răspuns:
[tex]11 + 17 + 23 + ... + 425 = \\ \\ = (6 \times 1 + 5) + (6 \times 2 + 5) + ... + (6 \times 70 + 5) = \\ \\ = 6 \times (1 + 2 + ... + 70) + 5 \times 70 = \\ \\ = 6 \times 70 \times 71 \div 2 + 350 = \\ \\ = 12425 + 350 = \\ \\ = 12775[/tex]
Succes! ♡︎♥︎♡︎
