5 It is given that, for \(n \geqslant 0\),
$$I _ { n } = \int _ { 0 } ^ { \frac { 1 } { 2 } } ( 1 - 2 x ) ^ { n } \mathrm { e } ^ { x } \mathrm {~d} x$$
- Prove that, for \(n \geqslant 1\),
$$I _ { n } = 2 n I _ { n - 1 } - 1$$
- Find the exact value of \(I _ { 3 }\).