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δ^{∥} = π - 2 \arctan [\sqrt{\frac{s i n^{2} α - N_{21}^{2}}{N_{21}^{2} \cos α}}] δ^{⊥} = - 2 \arctan [\sqrt{\frac{\sin^{2} α - N_{21}^{2}}{\cos α}}]

${\delta^\parallel = \pi - 2\arctan \bigg[ \sqrt{\frac{sin^2 \alpha - N_{21}^2}{N_{21}^2 \cos \alpha}} \bigg] \\ \delta^\perp = - 2 \arctan \bigg[ \sqrt{ \frac{\sin^2 \alpha -N_{21}^2}{\cos \alpha }} \bigg ]}$

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