For the form $\sqrt{b}$, I could just apply the recursive quadratic formula: $P_{k+1} = a_kQ_k - P_k$ $Q_{k+1} = \dfrac{d - P^2_{k+1}}{Q_k}$ $\alpha_k = \dfrac{P_k + \sqrt{d}}{Q_k}$ $a_k = \lfloor \alpha_k \rfloor$
In this case, we have a coefficient namely $a$, so what's $d$? Is it still $b$?
Thanks,