Si $x = \phi(t)$ y $y = \psi(t)$, entonces $\frac{d^2y}{dx^2}$ es:

1. [a.] $\frac{\phi' \psi'' - \psi' \phi''}{(\phi')^2}$
2. [b.] $\frac{\phi' \psi'' - \psi' \phi''}{(\phi')^3}$
3. [c.] $\frac{\phi''}{\psi''}$
4. [d.] $\frac{\psi''}{\phi''}$