Giải thích các bước giải:
\[\begin{array}{l}
a,D = \left( { - \infty ; + \infty } \right)\\
b,D = \left( { - \infty ;0} \right) \cup \left( {0; + \infty } \right)\\
c,D = \left[ {0; + \infty } \right)\\
d,D = \left[ { - 1;1} \right)\\
e,D = \left( { - \infty ;1} \right) \cup \left( {1; + \infty } \right)\\
f,\cos \frac{x}{3} \ne 0 \Leftrightarrow \frac{x}{3} \ne \frac{\pi }{2} + k\pi \Leftrightarrow x \ne \frac{{3\pi }}{2} + 3k\pi \\
g,\sin 2x \ne 0 \Leftrightarrow 2x \ne k\pi \Leftrightarrow x \ne \frac{{k\pi }}{2}\\
h,D = \left( { - \infty ; - 1} \right) \cup \left( { - 1;1} \right) \cup \left( {1; + \infty } \right)
\end{array}\]
