Differentiate two times a simple expression Let's say I have:
$$ y = -\frac{1}{\tan(x)} $$
How do you get a relation between $\mathrm{d}^2x$ and $\mathrm{d}^2y$ ?
What I know:
$$\mathrm{d}y = \frac{\mathrm{d}x}{\sin(x)^2}  $$

Hint: $$y^{(n)}(x)=\frac{d^ny(x)}{dx^n} \iff d^ny(x)=y^{(n)}(x)\space dx^n.$$
