Gọi $E,F,G$ là trung điểm $BC,AB,DC$
$\begin{array}{l} {Q_{\left( {O, - {{45}^o}} \right)}}\left( A \right) = F\\ {Q_{\left( {O, - {{45}^o}} \right)}}\left( B \right) = E\\ {Q_{\left( {O, - {{45}^o}} \right)}}\left( C \right) = G\\ \to {Q_{\left( {O, - {{45}^o}} \right)}}\left( {\Delta ABC} \right) = \Delta FEG \end{array}$