$\Delta{\varphi}=\varphi_2 - \varphi_1=\dfrac{\pi}{3}$
$tan\varphi =\dfrac{A_1 sin\varphi_1 + A_2 sin\varphi_2}{A_1 cos\varphi_1 + A_2 cos \varphi_2}≈0,587$
$A=\sqrt{A_1^2+A_2^2+2A_1 A_2 cos(\Delta{\varphi})}=\sqrt{61} cm$
$PT: x=\sqrt{61}cos(\pi t+0,587)$