$$\left. \begin{array} { l } { f ( x - 5 ) : x = x - 6 } \end{array} \right.$$
$\left\{\begin{matrix}\\x=\frac{\sqrt{f^{2}-8f+36}+f+6}{2}\text{, }&\text{unconditionally}\\x=\frac{-\sqrt{f^{2}-8f+36}+f+6}{2}\text{, }&f\neq 0\end{matrix}\right.$
