c
(c) \(\mu = \frac{{\sin \left({\frac{{A + {\delta _m}}}{2}} \right)}}{{\sin \frac{A}{2}}}\) ==> \(\sqrt 3 = \frac{{\sin \left({\frac{{60^\circ + {\delta _m}}}{2}} \right)}}{{\sin \frac{{60^\circ }}{2}}}\)

\( \Rightarrow \)\(\frac{{\sqrt 3 }}{2}\)=\(\sin \left({30^\circ + \frac{{{\delta _m}}}{2}} \right)\)\( \Rightarrow {\delta _m} = {60^o}\)