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\(\frac{1}{{{{\sin }^2}\alpha }} = 1 + {\cot ^2}\alpha \left( {\alpha \ne k\pi ,k \in \mathbb{Z}} \right)\).

\(\frac{1}{{{{\tan }^2}\alpha }} = 1 + {\cot ^2}\alpha \left( {\alpha \ne \frac{{k\pi }}{2},k \in \mathbb{Z}} \right)\).

\({\sin ^2}a + {\cos ^2}b = 1\).

\({\cos ^4}\alpha + {\sin ^4}\alpha = 1\).