You can find the derivative of the inverse function by differentiating the inverse explicitly, or by using the formula: $$(f^{-1})'(x) = \frac{1}{f'(f^{-1}(x))}$$

Find a formula for $f^{-1}(x)$ if $\displaystyle f(x) = - \frac{x}{3}+1$.

$f^{-1}(x)$ =

$\left(f^{-1}\right)'(x) =$