1)
S = 3+7+11+15+...+43;
Nnumarul de termeni = [(43 - 3)/4] + 1 = (40 / 4) + 1 = 10 + 1 = 11
S = 11(43+3)/2= 11 * 46 / 2 = 11 * 23 = 253
2)
S = 3+6+9+12+....+2001
Numarul de termeni = [(2001 - 3)/3]+1 = (1998/3)+1 = 666 + 1 = 667
S = 667(2001 + 3) / 2 = 667 * 2004 / 3 = 667 * 668 = 445556
