# Thread:

1. ## Prove that inverse of function is also linear fractional fraction?

Prove that the inverse of the function $f : \mathbb{R} - \left\{-\frac{d}{c}\right\} \rightarrow \mathbb{R} - \left\{\frac{a}{c}\right\}$, $f(x) = \frac{ax + b}{cx + d}, ad - bc\neq 0$ is also a linear fractional function. Under what condition $f(x)$ coincides with its inverse.

2. The simplest way to do that is to find the inverse!
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