Ba môi trường trong suốt (1), (2), (3) có thể đặt tiếp giáp nhau. Với cùng góc

$\begin{array}{l}\left\{(1) \rightarrow(2): \frac{\sin 60^{\circ}}{\sin 45^{0}}=\frac{\mathrm{n}_{2}}{\mathrm{n}_{1}}\right. \\(1) \rightarrow(3): \frac{\sin 60^{\circ}}{\sin 30^{\circ}}=\frac{\mathrm{n}_{3}}{\mathrm{n}_{1}} \\\Rightarrow\left\{\begin{array}{l}\frac{\sin 45^{\circ}}{\sin 30^{\circ}}=\frac{\mathrm{n}_{3}}{\mathrm{n}_{2}} \\(2) \rightarrow(3): \frac{\sin 60^{\circ}}{\sin \mathrm{r}}=\frac{\mathrm{n}_{3}}{\mathrm{n}_{2}}\end{array}\right. \\\Rightarrow \frac{\sin 60^{\circ}}{\sin \mathrm{r}}=\frac{\sin 45^{\circ}}{\sin 30^{\circ}} \Rightarrow \mathrm{r}=38^{\circ}\end{array}$