Find the general solution of the differential equation \(\frac{\mathrm d^2y}{\mathrm dx^2}=16-9x^2\), giving your answer in the form \(y=f(x)\).[3]
Given that \(u\) and \(t\) are related by \(\frac{\mathrm du}{\mathrm dt}=16-9u^2\), and that \(u=1\) when \(t=0\), find \(t\) in terms of \(u\), simplifying your answer.[5]