Explanation

(b) [image:9_image90.jpeg]
Following arguments lead us easily to the right choice
(i) Angle between any two lines is the same as the angle between their perpendiculars
$\therefore i = 30{^\circ}$
(ii)$\frac{1}{1.5} = \frac{\sin{30{^\circ}}}{\sin r}$
Or ${\ sin}{r = \frac{1.5}{2} = 0.75}$
Or $\ r = 48.6{^\circ}$
(iii)$\theta = r - i = 18.6{^\circ}$
Required angle $= 2 \times 18.6 = 37.2{^\circ}$