If rational functions have the form $f(x)=\frac{P(x)}{Q(x)}$, where $P(x)$ and $Q(x)$ are polynomials, how do you find the inverse of $f(x)$ when $P(x)$ and/or $Q(x)$ are polynomials of degree $2$ or higher?
for example: $\frac {3x+2}{x^2-4}, \frac {x^2-4}{3x+2}, \frac {x^2+2x-3}{x^3-4x}$