$\color{pink}{\text{$\textit{Bạn tham khảo:}$}}$

$\text{Từ vị trí x = 2 (cm) đến vị trí x = -4 (cm)}$ $\\$ $\Rightarrow$ $\text{$\Delta$t = $\frac{T}{4}$ + $\frac{T}{12}$ = $\frac{T}{3}$ = 0,4 (s)}$ $\\$ $\Rightarrow$ $\text{T = $\frac{6}{5}$ (s)}$ $\\$ $\text{Ta có: $\begin{cases} A = 4 (cm)\\T = \frac{6}{5} (s) => \omega = \frac{2\pi}{T} = \frac{5\pi}{3} (rad/s)\\\begin{cases} t = 0 (s)=> x = 2(cm)\\\text{chiều âm} \end{cases} => \varphi = \frac{\pi}{3} (rad) \end{cases}$}$ $\\$ $\Rightarrow$ $\text{x = 4cos($\frac{5\pi}{3}$.t + $\frac{\pi}{3}$) (cm)}$

$\color{pink}{\text{$\textit{Chúc bạn học tốt}$}}$