1. cos(2x + $\frac{2\pi}{3}$ ) + sin(x + $\frac{\pi}{3}$ ) = 0

Bởi

1. cos(2x + $\frac{2\pi}{3}$ ) + sin(x + $\frac{\pi}{3}$ ) = 0

0 bình luận về “1. cos(2x + $\frac{2\pi}{3}$ ) + sin(x + $\frac{\pi}{3}$ ) = 0”

  2. Đáp án:

    $\left[\begin{array}{l}x = \dfrac{\pi}{6} + k2\pi\\x = -\dfrac{\pi}{2} + k2\pi\\x = \dfrac{5\pi}{6} + k2\pi\end{array}\right.\quad (k \in \Bbb Z)$

    Giải thích các bước giải:

    $\cos\left(2x + \dfrac{2\pi}{3}\right) + \sin\left(x + \dfrac{\pi}{3}\right) = 0$

    $\Leftrightarrow \cos\left[2.\left(x + \dfrac{\pi}{3}\right)\right] + \sin\left(x + \dfrac{\pi}{3}\right) = 0$

    $\Leftrightarrow 2\sin^2\left(x + \dfrac{\pi}{3}\right) – \sin\left(x + \dfrac{\pi}{3}\right) -1 = 0$

    $\Leftrightarrow \left[\begin{array}{l}\sin\left(x + \dfrac{\pi}{3}\right) = 1\\\sin\left(x + \dfrac{\pi}{3}\right) = -\dfrac{1}{2}\end{array}\right.$

    $\Leftrightarrow\left[\begin{array}{l}x + \dfrac{\pi}{3} = \dfrac{\pi}{2} + k2\pi\\x + \dfrac{\pi}{3} = -\dfrac{\pi}{6} + k2\pi\\x + \dfrac{\pi}{3} = \dfrac{7\pi}{6} + k2\pi\end{array}\right.$

    $\Leftrightarrow\left[\begin{array}{l}x = \dfrac{\pi}{6} + k2\pi\\x = -\dfrac{\pi}{2} + k2\pi\\x = \dfrac{5\pi}{6} + k2\pi\end{array}\right.\quad (k \in \Bbb Z)$

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