Ta có: $\widehat{A}=180^{\circ}-50^{\circ}-30^{\circ}=100^{\circ};\widehat{C}=180^{\circ}-40^{\circ}-70^{\circ}=70^{\circ}$.
Như vậy $\widehat{A}+\widehat{C}=100^{\circ}+70^{\circ}=170^{\circ}$.
Ta có: $\widehat{A}=180^{\circ}-50^{\circ}-30^{\circ}=100^{\circ};\widehat{C}=180^{\circ}-40^{\circ}-70^{\circ}=70^{\circ}$.
Như vậy $\widehat{A}+\widehat{C}=100^{\circ}+70^{\circ}=170^{\circ}$.