\frac{E_{r 0}}{E_{i 0}} = \frac{1 - \tilde{n}}{1 + \tilde{n}} = \frac{(1 - n) + i κ}{(1 + n) - i κ}

${\frac{E_{r0}}{E_{i0}} =\frac{1- \tilde n}{1+\tilde n}= \frac{(1-n) + i \kappa}{(1+n) - i\kappa}}$

Error