Giải thích các bước giải:
Các hàm số đã cho xác định khi và chỉ khi:
\(\begin{array}{l}
a,\\
3 - \sin x \ge 0 \Leftrightarrow \sin x \le 3,\,\,\,\forall x\\
\Rightarrow TXD:\,\,\,\,\,D = R\\
b,\\
\sin x \ne 0 \Leftrightarrow x \ne k\pi \\
\Rightarrow TXD:\,\,\,\,D = R\backslash \left\{ {k\pi |k \in Z} \right\}\\
c,\\
\left\{ \begin{array}{l}
\dfrac{{1 - \sin x}}{{1 + \cos x}} \ge 0,\,\,\,\forall x\,\,\,\,\,\left( \begin{array}{l}
- 1 \le \sin x \le 1 \Rightarrow 1 - \sin x \ge 0\\
- 1 \le \cos x \le 1 \Rightarrow \cos x + 1 \ge 0
\end{array} \right)\\
1 + \cos x \ne 0
\end{array} \right.\\
\Rightarrow 1 + \cos x \ne 0\\
\Leftrightarrow \cos x \ne - 1\\
\Leftrightarrow x \ne \pi + k2\pi \\
\Rightarrow TXD:\,\,\,\,\,D = R\backslash \left\{ {\pi + k2\pi |k \in Z} \right\}\\
d,\\
y = \tan \left( {2x + \dfrac{\pi }{3}} \right)\\
\cos \left( {2x + \dfrac{\pi }{3}} \right) \ne 0\\
\Leftrightarrow 2x + \dfrac{\pi }{3} \ne \dfrac{\pi }{2} + k\pi \\
\Leftrightarrow 2x \ne \dfrac{\pi }{6} + k\pi \\
\Leftrightarrow x \ne \dfrac{\pi }{{12}} + \dfrac{{k\pi }}{2}\\
\Rightarrow TXD:\,\,\,\,\,\,D = R\backslash \left\{ {\dfrac{\pi }{{12}} + \dfrac{{k\pi }}{2}|k \in Z} \right\}
\end{array}\)
