#### Answer

$f(x)=7| x-3 |$

#### Work Step by Step

Using the properties of radicals, the given equation, $
f(x)=\sqrt[]{49(x-3)^2}
,$ simplifies to
\begin{array}{l}\require{cancel}
f(x)=\sqrt[]{\left[7(x-3) \right]^2}
\\\\
f(x)=| 7(x-3) |
\\\\
f(x)=7| x-3 |
\end{array}