c
(c) By prism formula \(n = \frac{{\sin \frac{{A + A}}{2}}}{{\sin \frac{A}{2}}} = \frac{{2\sin \frac{A}{2}\cos \frac{A}{2}}}{{\sin \frac{A}{2}}}\)

\(\therefore \) \(\cos \frac{A}{2} = \frac{n}{2} = \frac{{1.5}}{2} = 0.75 = \cos {41^o}\) ==> \(A = {82^o}\)