In textbook "Wireless Communications Principles and Practice" by Theodore S. Rappaport, the expression of Fresnel reflection coefficient ($\Gamma$) for parallel polarization is given as $\Gamma_{||} = \frac{E_r}{E_i} = \frac{\eta_2 \text{sin} \theta_t- \eta_1 \text{sin} \theta_i}{\eta_2 \text{sin} \theta_t+ \eta_1 \text{sin} \theta_i}$...(1).
However, I did not find the derivation of this eq. (1) in the same text book.
Upon checking the internet, I found the new expression of $\Gamma$ as
$\Gamma_{||} = \frac{E_r}{E_i} = \frac{\eta_2 \text{cos} \theta_t- \eta_1 \text{cos} \theta_i}{\eta_2 \text{cos} \theta_t+ \eta_1 \text{cos} \theta_i}$...(2).
I am getting doubt due to presence of "sin" and "cos" in eq. (1), (2) respectively.
My query is that are these two equations (eq.(1) and eq.(2)) same?
Any help in this regard will be highly appreciated.