\[f(x) = \left\{ \begin{matrix} x^{2};\ \ 0 \leq x \leq 1 \\ 2x - 1;\ \ x > 1 \\ \end{matrix} \right.\ \]
\[0 \leq \frac{1}{2} \leq 1:\]
\[f\left( \frac{1}{2} \right) = x^{2} = \left( \frac{1}{2} \right)^{2} = \frac{1}{4}.\]