Toán Lớp 11: Tìm TXĐ của hs sau :y= tan( pi/2 cosx)
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Toán Lớp 11: Tìm TXĐ của hs sau :y= tan( pi/2 cosx)
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\cos \left( {\dfrac{\pi }{2}\cos x} \right) \ne 0\\
\Leftrightarrow \dfrac{\pi }{2}\cos x \ne \dfrac{\pi }{2} + k\pi \\
\Leftrightarrow \dfrac{1}{2}\cos x \ne \dfrac{1}{2} + k\\
\Leftrightarrow \cos x \ne 2k + 1\,\,\,\,\,\left( {k \in Z} \right)\\
– 1 \le \cos x \le 1\\
\Leftrightarrow – 1 \le 2k + 1 \le 1\\
\Leftrightarrow – 2 \le 2k \le 0\\
\Leftrightarrow – 1 \le k \le 0\\
k \in Z \Rightarrow k \in \left\{ { – 1;0} \right\}\\
\Rightarrow \left\{ \begin{array}{l}
\cos x \ne – 1\\
\cos x \ne 1
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x \ne \pi + l2\pi \\
x \ne l2\pi
\end{array} \right. \Leftrightarrow x \ne l\pi \,\,\,\,\,\left( {l \in Z} \right)
\end{array}\)