6 The polynomial \(\mathrm { p } ( x )\) is defined by
$$\mathrm { p } ( x ) = 6 x ^ { 3 } + a x ^ { 2 } - 4 x - 3$$
where \(a\) is a constant. It is given that \(( x + 3 )\) is a factor of \(\mathrm { p } ( x )\).
- Find the value of \(a\).
- Using this value of \(a\), factorise \(\mathrm { p } ( x )\) completely.
- Hence solve the equation \(\mathrm { p } ( \operatorname { cosec } \theta ) = 0\) for \(0 ^ { \circ } < \theta < 360 ^ { \circ }\).