Toán Lớp 11: mọi người ơi :sin4x=cos2x làm sao vậy ạ
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Toán Lớp 11: mọi người ơi :sin4x=cos2x làm sao vậy ạ
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\sin 4x = \cos 2x\\
\Leftrightarrow \cos 2x = \cos \left( {\dfrac{\pi }{2} – 4x} \right)\\
\Leftrightarrow \left[ \begin{array}{l}
2x = \dfrac{\pi }{2} – 4x + k2\pi \\
2x = 4x – \dfrac{\pi }{2} + k2\pi
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = \dfrac{\pi }{6} + \dfrac{{k\pi }}{3}\\
2x = \dfrac{\pi }{2} – k2\pi
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = \dfrac{\pi }{6} + \dfrac{{k\pi }}{3}\\
x = \dfrac{\pi }{4} – k\pi
\end{array} \right.\left( {k \in \mathbb{Z}} \right)
\end{array}$