3 The polynomial \(2 x ^ { 3 } + a x ^ { 2 } - 4\) is denoted by \(\mathrm { p } ( x )\). It is given that ( \(x - 2\) ) is a factor of \(\mathrm { p } ( x )\).
- Find the value of \(a\).
When \(a\) has this value,
- factorise \(\mathrm { p } ( x )\),
- solve the inequality \(\mathrm { p } ( x ) > 0\), justifying your answer.