a+a*q^3=30 a(1+q^3)=30 a(1+q)(1-q+q^2)=30 10(1-q+q^2)/q=30
aq+aq^2=10 aq(1+q)=10
1-q+q^2=3q
q^2-4q+1=0
q=2+sqr(3)
q=2-sqrt(3)
a=10/(2+sqrt(3))(3+sqrt(3))=10/(9+5sqrt(3))
a=10/(2-sqrt(3))(3-sqrt(3))=10/(3-sqrt(3))=10*(3+sqrt(3))/6=5*(3+sqrt(3))/3
