Trả lời bởi giáo viên
Đáp án A: $\left. \begin{array}{l}\tan (\pi - \alpha ) = - \tan \alpha \\\tan (\dfrac{\pi }{2} - \alpha ) = \cot \alpha \end{array} \right\} \Rightarrow \tan (\pi - \alpha ) \ne \tan (\dfrac{\pi }{2} - \alpha )$. A sai
Đáp án B: $\left. \begin{array}{l}\tan (\dfrac{\pi }{2} - \alpha ) = \cot \alpha \\\tan ( - \alpha ) = - \tan \alpha \end{array} \right\} \Rightarrow \tan (\dfrac{\pi }{2} - \alpha ) \ne \tan ( - \alpha )$. B sai
Đáp án C: $\left. \begin{array}{l}\tan (\pi - \alpha ) = - \tan \alpha \\\tan (\dfrac{\pi }{2} + \alpha ) = - \cot \alpha \end{array} \right\} \Rightarrow \tan (\pi - \alpha ) \ne \tan (\dfrac{\pi }{2} + \alpha )$ . C sai
Đáp án D: $\left. \begin{array}{l}\tan (\dfrac{\pi }{2} - \alpha ) = \cot \alpha \\\cot (\pi + \alpha ) = \cot \alpha \end{array} \right\} \Rightarrow \tan (\dfrac{\pi }{2} - \alpha ) = \cot (\pi + \alpha )$. D đúng