3.12 Symbols left and right can be applied to

$$\left( \dfrac{1}{2} \right), \left[ \dfrac{1}{2} \right], 
\left\{ \dfrac{1}{2} \right\}, \left| \dfrac{1}{2} \right|$$ 
\[ \left( \dfrac {1}{2} \right), \left[ \dfrac {1}{2} \right], \left\{ \dfrac {1}{2} \right\} , \left| \dfrac {1}{2} \right| \]