$${\frac{E_{r0}^\perp}{E_{i0}^\perp} = \frac{\cos \alpha -\frac{n_2}{n_1} \cos \gamma}{\cos \alpha + \frac{n_2}{n_1} \cos \gamma} = \frac{\cos \alpha - \frac{\sin \alpha}{\sin \gamma} \cos \gamma }{\cos\alpha + \frac{\sin \alpha }{\sin \gamma} \cos \gamma}}$$