Answer
$f^{-1}(x) = 0.4^{x}$
Work Step by Step
$f(x) =\log_{0.4} x$
Let $f(x) = y$
$y = \log_{0.4} x$
Swap the $x$ and $y$ variable to find the inverse:
$x =\log_{0.4} y$
$y =0.4^{x}$
$f^{-1}(x) = 0.4^{x}$
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