12. If the function $f(x)$ defined on $\mathbf{R}$ is an even function, and $f(2+x)=f(2-x)$. Also, when $x \in$ $(0,2)$, $f(x)=\frac{1}{x}$, then when $x \in(-4,-2)$, the analytical expression of $f(x)$ is . $\qquad$
12. $\frac{1}{x+4}$.
The graph of $f(x)$ has two axes of symmetry, $x=0$ and $x=2$. To obtain the graph of the given function, simply shift the graph of $y=\frac{1}{x}$ to the left by 4 units.