\(x=2\cos\left(5\pi t -\dfrac{2\pi}{3}\right)\)
b)
Gốc thời gian được chọn lúc t=0
\(\Rightarrow x=2\cos\left(5\pi .0-\dfrac{2\pi}{3}\right)=-1(cm)\\c)\\v=A\omega\cos\left(\omega t+\varphi +\dfrac{\pi}{2}\right)\\\Rightarrow v=10\pi\cos\left(5\pi t-\dfrac{2\pi}{3}+\dfrac{\pi}{2}\right)=10\pi\cos\left(5\pi t-\dfrac{\pi}{6}\right)\\t=1(s)\Rightarrow \begin{cases} x=2\cos\left(5\pi -\dfrac{2}{3}\pi\right)=1(cm)\\v=10\pi\cos\left(5\pi .1-\dfrac{\pi}{6}\right)=-5\sqrt{3}(cm/s)\end{cases}\)
