$\left\{ \begin{gathered}
  {x_M} = \frac{{{x_A} + {x_B}}}{2} = \frac{{\frac{1}{3} + \frac{2}{3}}}{2} = \frac{1}{2} \hfill \cr 
  {y_M} = \frac{{{y_A} + {y_B}}}{2} = \frac{{ - 2 + 3}}{2} = \frac{1}{2} \hfill \cr 
 \end{gathered}  \right. \Rightarrow M \left( {\frac{1}{2},\frac{1}{2}} \right)$
 
${m_D} = {m_{D'}} =  - \frac{a}{b} = \frac{1}{2}$
$D'$معادله :$y - {y_M} = m\left( {x - {x_M}} \right) \Rightarrow y - \frac{1}{2} = \frac{1}{2}\left( {x - \frac{1}{2}} \right) \Rightarrow y = \frac{1}{2}x + \frac{1}{4}$