$\Rightarrow 6x=360{}^\circ \Rightarrow x=60{}^\circ \Rightarrow \widehat{A}=\frac{\overset\frown{DBC}}{2}$ محاطی  $\Rightarrow \overset\frown{DBC}=4x=4\times 60{}^\circ =240{}^\circ \Rightarrow \widehat{A}=\frac{240{}^\circ }{2}=120{}^\circ $