Toán Lớp 11: Giải cos3x+cos2x=0
Giúp mk gấp vs ạ
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Toán Lớp 11: Giải cos3x+cos2x=0
Giúp mk gấp vs ạ
Comments ( 1 )
\cos 3x + \cos 2x = 0\\
\Leftrightarrow \cos 3x = – \cos 2x\\
\Leftrightarrow \cos 3x = \cos \left( {\pi – 2x} \right)\\
\Leftrightarrow \left[ \begin{array}{l}
3x = \pi – 2x + k2\pi \\
3x = 2x – \pi + k2\pi
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
5x = \pi + k2\pi \\
x = – \pi + k2\pi
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = \dfrac{\pi }{5} + \dfrac{{k2\pi }}{5}\\
x = – \pi + k2\pi
\end{array} \right.\left( {k \in \mathbb{Z}} \right)
\end{array}$