Phương trình nào sau đây biểu thị cho dao động điều hòa?

$x = 6cos\left( {\dfrac{\pi }{3}t - \dfrac{\pi }{3}} \right)cm$

$x = 6cos\left( {\dfrac{\pi }{3}t + \dfrac{\pi }{6}} \right)cm$

$x = 6cos\left( {\pi t - \dfrac{\pi }{6}} \right)cm$

$x = 6cos\left( {\dfrac{{2\pi }}{3}t - \dfrac{{5\pi }}{6}} \right)cm$

$\dfrac{\pi }{2} < \varphi < \pi$

$- \dfrac{\pi }{2} < \varphi < 0$

$- \pi < \varphi <  - \dfrac{\pi }{2}$  

$0 < \varphi < \dfrac{\pi }{2}$

$- \dfrac{\pi }{3}$

$\dfrac{\pi }{3}$

$- \dfrac{{2\pi }}{3}$

$\dfrac{{2\pi }}{3}$

${\rm{x}} = 16c{\rm{os}}\left( {2\pi t - \dfrac{\pi }{2}} \right)(cm)$

${\rm{x}} = 16c{\rm{os}}\left( {2\pi t + \dfrac{\pi }{2}} \right)(cm)$

${\rm{x}} = 8c{\rm{os}}\left( {2\pi t + \dfrac{\pi }{2}} \right)(cm)$

${\rm{x}} = 8c{\rm{os}}\left( {2\pi t - \dfrac{\pi }{2}} \right)(cm)$

$x = 2c{\rm{os}}\left( {\pi t - \dfrac{\pi }{2}} \right)cm$

$x = 4c{\rm{os}}\left( {2\pi t - \dfrac{\pi }{2}} \right)cm$

$x = 2c{\rm{os}}\left( {\pi t + \dfrac{\pi }{2}} \right)cm$

$x = 4c{\rm{os}}\left( {\pi t - \dfrac{\pi }{2}} \right)cm$

$x = 4c{\rm{os}}\left( {\dfrac{\pi }{3}t - \dfrac{\pi }{3}} \right)cm$

$x = 4c{\rm{os}}\left( {\dfrac{\pi }{3}t + \dfrac{\pi }{6}} \right)cm$

$x = 4c{\rm{os}}\left( {\pi t - \dfrac{\pi }{6}} \right)cm$

$x = 4c{\rm{os}}\left( {\dfrac{{2\pi }}{3}t - \dfrac{{5\pi }}{6}} \right)cm$