Let $g(x) = 4x + 1$.
Find $f(x)$, given that the equation $(g \circ f)(x) = x + 5$ is true for all values of $x$.
From my text, it looks like this would be expressed as $g[f(x)]$, but I don't see how you can determine the definition of $f(x)$. Do I need to assume a value of x and work backwards through the problem?