Let a ray AO incident on the glass slab at O and is reflected along OB and refracted along OC having angle of incidence i and angle of refraction r as shown in the given figure.
From the figure
i + 90° + r = 180°
or i + r = 90°
or r = 90° - i
From Snell's law
µ = \(\frac{sin\ i}{\sin r} = \frac{sin\ i}{sin (90-i)} = \frac{sin\ i}{cos\ i}\)
= tan i
or i = tan-1 µ = tan -1 (1.62) = 59°19'