Answer:
The answer is "1.26".
Explanation:
[tex]D=18^{\circ}[/tex]
The refractive index is:
[tex]\to \mu=2\sin(30^{\circ}+\frac{D}{2})\\\\[/tex]
[tex]=2\sin(30^{\circ}+\frac{18^{\circ}}{2})\\\\=2\sin(30^{\circ}+9^{\circ})\\\\=2\sin(30^{\circ}+9^{\circ})\\\\=2\sin(39^{\circ})\\\\=2 \times 0.63\\\\=1.26[/tex]
