When $x=\frac{A}{2}, \Rightarrow \frac{A}{2}=A \cos \left(\omega t+\phi_{1}\right)$
or $60^{\circ}=\omega t+\phi_{1} \ldots . .(1)$
When $x=-\frac{A}{\sqrt{2}}, \Rightarrow-\frac{A}{\sqrt{2}}=A \cos \left(\omega t+\phi_{1}\right)$
or $225^{\circ}=\omega t+\phi_{2} \ldots . .(2)$
$(2)-(1) \Rightarrow \phi_{2}-\phi_{1}=225-60=165^{\circ}$
also $x=A \sin (\omega t+\phi)$
When $x=\frac{A}{2}, \Rightarrow \frac{A}{2}=A \sin \left(\omega t+\phi_{1}\right)$
or $30^{\circ}=\omega t+\phi_{1} \ldots . .(1)$
When $x=-\frac{A}{\sqrt{2}}, \Rightarrow-\frac{A}{\sqrt{2}}=A \sin \left(\omega t+\phi_{1}\right)$
or $225^{\circ}=\omega t+\phi_{2} \ldots . .(2)$
$(2)-(1) \Rightarrow \phi_{2}-\phi_{1}=225-30=195^{\circ}$
