v 4.12

\frac{E_{r 0}^{∥}}{E_{i 0}^{∥}} = - \frac{N_{21} \cos α - \cos γ}{N_{21} \cos α + \cos γ}

${\frac{E_{r0}^\parallel}{E_{i0}^\parallel} = - \frac{N_{21} \cos \alpha - \cos \gamma}{N_{21} \cos \alpha + \cos \gamma}}$

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