$\begin{array}{l} a.{\left( {x - \frac{3}{2}} \right)^2} = \frac{9}{{16}}\\ = > \left[ \begin{array}{l} x - \frac{3}{2} = \frac{3}{4}\\ x - \frac{3}{2} = \frac{{ - 3}}{4} \end{array} \right.\\ = > \left[ \begin{array}{l} x = \frac{3}{4} + \frac{3}{2}\\ x = \frac{{ - 3}}{4} + \frac{3}{2} \end{array} \right.\\ = > \left[ \begin{array}{l} x = \frac{9}{4}\\ x = \frac{3}{4} \end{array} \right.\\ Vay:S = \{ \frac{9}{4};\frac{3}{4}\} \\ b.{\left( {x + \frac{1}{2}} \right)^2} = \frac{1}{{16}}\\ = > \left[ \begin{array}{l} x + \frac{1}{2} = \frac{1}{4}\\ x + \frac{1}{2} = \frac{{ - 1}}{4} \end{array} \right.\\ = > \left[ \begin{array}{l} x = \frac{1}{4} - \frac{1}{2}\\ x = \frac{{ - 1}}{4} - \frac{1}{2} \end{array} \right.\\ = > \left[ \begin{array}{l} x = \frac{{ - 1}}{4}\\ x = \frac{{ - 3}}{4} \end{array} \right.\\ Vay:S = \{ \frac{{ - 1}}{4};\frac{{ - 3}}{4}\} \end{array}$