TeX source:
\begin{array}{rcl} f(4) &=& \dfrac{1}{2}\left(4-\dfrac{3}{2}\right)^2-\dfrac{25}{8} \cr&=& \dfrac{1}{2}\left(\dfrac{5}{2}\right)^2-\dfrac{25}{8} \cr&=& \dfrac{1}{2}\cdot\dfrac{25}{4}-\dfrac{25}{8} \cr&=& 0 \end{array}