Câu 4.1 : Ta có :
a. x+ $120^{\circ}$ + $35^{\circ}$= $180^{\circ}$ => x= $180^{\circ}$- $35^{\circ}$- $120^{\circ}$ = $25^{\circ}$
b. y+ $60^{\circ}$ + $70^{\circ}$= $180^{\circ}$ => y= $180^{\circ}$- $70^{\circ}$- $60^{\circ}$ = $50^{\circ}$
c. z+ $90^{\circ}$ + $55^{\circ}$= $180^{\circ}$ => y= $180^{\circ}$- $90^{\circ}$- $55^{\circ}$ = $35^{\circ}$