Toán Lớp 11: Phương trình lượng giác cơ bản:
Sin ²x -3/4=0
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Toán Lớp 11: Phương trình lượng giác cơ bản:
Sin ²x -3/4=0
Comments ( 2 )
\quad \sin^2x – \dfrac34 = 0\\
\Leftrightarrow \dfrac{1 – \cos2x}{2} – \dfrac34 = 0\\
\Leftrightarrow \cos2x = -\dfrac12\\
\Leftrightarrow \left[\begin{array}{l}2x =\dfrac{2\pi}{3} + k2\pi\\2x = – \dfrac{2\pi}{3} + k2\pi\end{array}\right.\\
\Leftrightarrow \left[\begin{array}{l}x = \dfrac{\pi}{3} + k\pi\\x = -\dfrac{\pi}{3} + k\pi\end{array}\right.\quad (k\in\Bbb Z)\\
\text{Vậy}\ S = \left\{\dfrac{\pi}{3} + k\pi;\ -\dfrac{\pi}{3} + k\pi\ \Bigg|\ k\in\Bbb Z\right\}
\end{array}\)