9. (a) (i) Expand \(\left( \cos \frac { \theta } { 3 } + i \sin \frac { \theta } { 3 } \right) ^ { 3 }\).
(ii) Hence, by using de Moivre's theorem, show that \(\cos \theta\) can be expressed as $$4 \cos ^ { 3 } \frac { \theta } { 3 } - 3 \cos \frac { \theta } { 3 }$$ (b) Hence, or otherwise, find the general solution of the equation \(\frac { \cos \theta } { \cos \frac { \theta } { 3 } } = 1\).