3 The polynomial \(\mathrm { p } ( x )\) is defined by
$$\mathrm { p } ( x ) = x ^ { 3 } - 3 a x + 4 a$$
where \(a\) is a constant.
- Given that \(( x - 2 )\) is a factor of \(\mathrm { p } ( x )\), find the value of \(a\).
- When \(a\) has this value,
(a) factorise \(\mathrm { p } ( x )\) completely,
(b) find all the roots of the equation \(\mathrm { p } \left( x ^ { 2 } \right) = 0\).