B^1+b^2+b^3=26. b^4+b^5+b^6=702. Найти S^5

Question

B^1+b^2+b^3=26. b^4+b^5+b^6=702. Найти S^5

Answer 1

B1(q^2+q+1)=26
b1q^3(q^2+q+1)=702
Делим
702/26=27
q^3=27
q=3
b1=26/q^2+q+1
b1=2
S5=b1(q^n-1)/q-1
S5=242