Le rezolvi cu progresii geometrice;
a) b1=1/3
q=b2/b1= 1/3
Sn = b1*(q^n - 1 ) / (q-1) = 1/3 * ( (1/3)^6 - 1) / (2/3-1) = ((1/3^6)-1)/ -2
b) b1= 1/2
q= 1/2
Sn = 1/2*((1/2)^6 - 1) / (1/2-1) = ((1/2)^6 -1) / -1
