A stressed spring moves with harmonic motion of period \(T\). Its elongation at time \(t_{1}=T / 8\) \(\mathrm{s}\) is equal to \(x_{1}=2 \mathrm{~cm}\), and its velocity and acceleration are equal to \(v_{1}=-4 \mathrm{~cm} / \mathrm{s}\) and \(a_{1}=-8 \mathrm{~cm} / \mathrm{s}^{2}\), respectively. Determine the parameters of the equation of motion of the spring \(x(t)=x_{0} \cos (\omega t+\phi)\).