Tại sao w' bằng 2w help meeeeeeeeeee

\(\begin{cases} W_d=\dfrac{1}{2}mv^2\\v=-A\omega \sin(\omega t +\varphi)\end{cases}\Rightarrow W_d=\dfrac{1}{2}m.A^2\omega^2\sin^2(\omega t+\varphi)\)

Đặt \(W=\dfrac{1}{2}m\omega^2A^2\)

\(\Rightarrow W_d=W\left[\dfrac{1-\cos(2\omega t+2\varphi)}{2}\right]\\=\dfrac{W}{2}-\dfrac{W}{2}\cos(\underbrace{\begin{array}{|c|c|c|}\hline 2\omega t\\\hline\end{array}}_{\omega't}+2\varphi)\\\Rightarrow \omega'=2\omega\)