## Precalculus (6th Edition)

$-3$
See: Inverse Function, p.409. Let $f$ be a one-to-one function. Then $g$ is the inverse function of $f$ if $(f\circ g)(x)=x$ for every $x$ in the domain of $g$, and $(g\circ f)(x)=x$ for every $x$ in the domain of $f$. ----------------- $f^{-1}(6)=f^{-1}[f(-3)]=f^{-1}\circ f(-3)=$ by the definition, $= -3$