A curve \(C\) has equation \(\tan y=x\), for \(x\gt 0\).
(i) Use implicit differentiation to show that
\(\frac{\mathrm{d}^{2} y}{\mathrm{~d} x^{2}}=-2 x\left(\frac{\mathrm{~d} y}{\mathrm{~d} x}\right)^{2} .\)
(ii) Hence find the value of \(\frac{\mathrm{d}^{2} y}{\mathrm{~d} x^{2}}\) at the point \(\left(1, \frac{1}{4} \pi\right)\) on \(C\).