Cho góc lượng giác alpha . Chọn khẳng định đúng trong các khẳng định sau

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

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

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

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