Let  \[f(x) =
\begin{cases}
k(x) &\text{if }x>0, \\
-\frac1{2x}&\text{if }x< 0\\
0&\text{if }x=0.
\end{cases}
\]Find the function $k(x)$ such that $f(x)$ is its own inverse function.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Let  \[f(x) =
\begin{cases}
k(x) &\text{if }x>0, \\
-\frac1{2x}&\text{if }x< 0\\
0&\text{if }x=0.
\end{cases}
\]Find the function $k(x)$ such that $f(x)$ is its own inverse function.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
-\frac1{2x}
Let  \[f(x) =
\begin{cases}
k(x) &\text{if }x>0, \\
-\frac1{2x}&\text{if }x< 0\\
0&\text{if }x=0.
\end{cases}
\]Find the function $k(x)$ such that $f(x)$ is its own inverse function.
train