Formula: Sn = n(a1 + an)/2
a)
S1 = 1+2+3+...+45 = 45(1+45)/2 = 45*46/2 = 45*23 = 1035 = 3*3*5*23
S2 = 1+2+3+...+69 = 69(1+69)/2 = 69*70/2 = 69*35 = 2415 = 3*5*7*23
(1035; 2415) = 3*3*5*7*23 = 7245
[1035; 2415] = 3*5*23 = 345
Punctul b se rezolva in acelasi mod. Sper ca nu am gresit la cmmdc si cmmmc. In caz afirmativ astept corectari! Bft!