Câu 125
Ta có
$y = \sin \left( \dfrac{\pi}{3} - \dfrac{x}{2} \right)$
Suy ra
$y' = \cos \left( \dfrac{\pi}{3} - \dfrac{x}{2} \right) . \left( -\dfrac{1}{2} \right)$
Xét ptrinh $y' = 0$ ta có
$\cos \left( \dfrac{\pi}{3} - \dfrac{x}{2} \right) . \left( -\dfrac{1}{2} \right) = 0$
$<-> \cos \left( \dfrac{\pi}{3} - \dfrac{x}{2} \right) = 0$
$<-> \dfrac{\pi}{3} - \dfrac{x}{2} = \dfrac{\pi}{2} + k\pi$
$<-> \dfrac{x}{2} = -\dfrac{\pi}{6} + k\pi$
$<-> x = -\dfrac{\pi}{3} + 2k\pi$
Vậy nghiệm của $y' = 0$ là $-\dfrac{\pi}{3} + 2k\pi$.
Đáp án C.
