\[f(x) = \sqrt{x - 1} + \sqrt{1 - x}\text{\ \ }\]
\[\left\{ \begin{matrix}
x - 1 \geq 0 \\
1 - x \geq 0 \\
\end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\left\{ \begin{matrix}
x \geq 1 \\
x \leq 1 \\
\end{matrix} \right.\ \]
\[D(f) = 1\]
\[E(f) = f(1) = 0.\]