b
(b) \(\mu = \frac{{\sin \left({\frac{{A + {\delta _m}}}{2}} \right)}}{{\sin \left({\frac{A}{2}} \right)}}\)

\( \Rightarrow \sqrt 2 \mu = \frac{{\sin \left({\frac{{60 + {\delta _m}}}{2}} \right)}}{{\sin \left({\frac{{60}}{2}} \right)}}\)

\( \Rightarrow \sqrt 2 \times \sin 30 = \sin \,\left({\frac{{60 + {\delta _m}}}{2}} \right) \Rightarrow \sin {45^o}\)

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