For δmin $\begin{aligned}
& \mathrm{i}=\mathrm{e} \
& \mathrm{r}_1=\mathrm{r}2=\frac{\mathrm{A}}{2} \
& \frac{\delta{\min }}{\mathrm{A}}=1 \
& \frac{2 \mathrm{i}-\mathrm{A}}{\mathrm{A}}=1 \
& \
& 2 \mathrm{i}=2 \mathrm{~A} \
& \mathrm{i}=\mathrm{A}
\end{aligned}$
Snell's law $\begin{aligned}
& 1 \times \sin i=\mu \sin r \
& \sin i=\mu \sin \left(\frac{A}{2}\right) \
& \sin A=\mu \sin \left(\frac{A}{2}\right) \
& 2 \sin \frac{A}{2} \cos \frac{A}{2}=\sqrt{3} \sin \left(\frac{A}{2}\right) \
& \cos \left(\frac{A}{2}\right)=\frac{\sqrt{3}}{2} \
& \therefore \frac{A}{2}=30^{\circ} \
& \therefore A=60^{\circ}
\end{aligned}$