3. The first four terms in the series expansion of \(( 1 + a x ) ^ { n }\) in ascending powers of \(x\) are
$$1 - 4 x + 24 x ^ { 2 } + k x ^ { 3 }$$
where \(a , n\) and \(k\) are constants and \(| a x | < 1\).
- Find the values of \(a\) and \(n\).
- Show that \(k = - 160\).