Đáp án:
\(TXD:D = R\backslash \left\{ {\dfrac{\pi }{2} + k\pi } \right\}\)
Giải thích các bước giải:
\(\begin{array}{l}
DK:\left\{ \begin{array}{l}
\cos x \ne 0\\
{\tan ^2}x + 5 \ne 0
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x \ne \dfrac{\pi }{2} + k\pi \\
{\tan ^2}x \ne - 5\left( {ld} \right)\forall x
\end{array} \right.\\
\to x \ne \dfrac{\pi }{2} + k\pi \left( {k \in Z} \right)
\end{array}\)
\( \to TXD:D = R\backslash \left\{ {\dfrac{\pi }{2} + k\pi } \right\}\)
