5 A curve has parametric equations
$$x = 2 t + t ^ { 2 } , \quad y = 2 t ^ { 2 } + t ^ { 3 }$$
- Express \(\frac { \mathrm { d } y } { \mathrm {~d} x }\) in terms of \(t\) and find the gradient of the curve at the point \(( 3 , - 9 )\).
- By considering \(\frac { y } { x }\), find a cartesian equation of the curve, giving your answer in a form not involving fractions.