a, x=5sin(2\(\pi\) t + \(\frac{\pi}{6}\) ) = 5cos(\(\frac{\pi}{2}-\left(2\pi t+\frac{\pi}{6}\right)\) = \(5\cos\left(2\pi t-\frac{\pi}{3}\right)\)

\(v=5.2\pi\cos\left(2\pi t-\frac{\pi}{3}+\frac{\pi}{2}\right)=10\pi\cos\left(2\pi t+\frac{\pi}{6}\right)\)

\(a=-\left(2\pi\right)^2.5\cos\left(2\pi t+\frac{\pi}{6}+\frac{\pi}{2}\right)=-20\pi^2\cos\left(2\pi t+\frac{2\pi}{3}\right)\)

Có: \(x=5\cos\left(2\pi.5-\frac{\pi}{3}\right)=2,5\) (cm)

\(v=10\pi\cos\left(2\pi.5+\frac{\pi}{6}\right)\thickapprox27,2\) (cm/s)

\(a=-20\pi^2\cos\left(2\pi.5+\frac{2\pi}{3}\right)\thickapprox-99\) (cm/\(s^2\) )

b, Có: \(120^{o}=\frac{2\pi}{3}rad\)

Có: \(x=5\cos\left(\frac{2\pi}{3}\right)=-2,5\) (cm)

\(v=10\pi\cos\left(\frac{2\pi}{3}\right)=-5\pi\thickapprox-15,7\) (cm/s)

\(a=-20\pi^2\cos\left(\frac{2\pi}{3}\right)\thickapprox98,7\) (cm/\(s^2\) )