Question 94
A fixed point of a function $f$ is a value of $x$ for which $f(x)=x$. Let $f$ be the quadratic function defined by $f(x)=x^{2}-c x+c$ where $c \in \mathbb{R}$. Find, in interval notation, the set consisting of all values of $c$ for which $f \circ f$ has four distinct fixed points.