v 4.14

\frac{E_{t 0}^{∥}}{E_{t 0}^{∥}} = - \frac{2 \sin γ \cos α}{\sin (α + γ) \cos (α - γ)}

${\frac{E_{t0}^\parallel}{E_{t0}^\parallel} = - \frac{2 \sin \gamma \cos \alpha}{\sin (\alpha + \gamma) \cos (\alpha - \gamma)}}$

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