خطا
$\overset{\vartriangle }{\mathop{OAB}}\,:{{\widehat{O}}_{1}}=\widehat{A}+\widehat{B}\xrightarrow{\widehat{B}=2\widehat{A}}75=3\widehat{A}\Rightarrow \widehat{A}=25{}^\circ ,\widehat{B}=50{}^\circ $ $\begin{align} & \overset{\vartriangle }{\mathop{OBD}}\,:OB=OD\Rightarrow \widehat{B}=\widehat{D}=50{}^\circ \Rightarrow {{\widehat{O}}_{2}}=180-\left( \widehat{B}+\widehat{D} \right)=80{}^\circ \\ & {{\widehat{O}}_{3}}=180-\left( {{\widehat{O}}_{1}}+{{\widehat{O}}_{2}} \right)=180-\left( 75+80 \right)=25{}^\circ \Rightarrow \overset\frown{DE}=25{}^\circ \\ \end{align}$