b_n^2=b_(n-1) * b_(n+1)
b3^2=b2 * b4,
b4=b3^2/b2,
b4=(3-5√3)^2/(5√3-14)=(9-30√3+75)/(5√3-14)=(84-30√3)/(5√3-14)=-6(5√3-14)/(5√3-14)=-6
