9 Using the substitution \(u = \cos \theta\), or any other method, find \(\int \sin \theta \cos ^ { 2 } \theta d \theta\). It is given that \(I _ { n } = \int _ { 0 } ^ { \frac { 1 } { 2 } \pi } \sin ^ { n } \theta \cos ^ { 2 } \theta \mathrm {~d} \theta\), for \(n \geqslant 0\). Show that, for \(n \geqslant 2\), $$I _ { n } = \frac { n - 1 } { n + 2 } I _ { n - 2 }$$ Hence find the exact value of \(\int _ { 0 } ^ { \frac { 1 } { 2 } \pi } \sin ^ { 4 } \theta \cos ^ { 2 } \theta d \theta\).