4.
\(\mathrm { f } ( x ) = - 4 x ^ { 3 } + a x ^ { 2 } + 9 x - 18\), where \(a\) is a constant.
Given that ( \(x - 2\) ) is a factor of \(\mathrm { f } ( x )\),
- find the value of \(a\),
- factorise \(\mathrm { f } ( x )\) completely,
- find the remainder when \(\mathrm { f } ( x )\) is divided by ( \(2 x - 1\) ).