a) $\alpha$ = $135^{\circ}$ b) $\alpha$ = $0^{\circ}$ hoặc $\alpha$ = $180^{\circ}$
c) $\alpha$ = $45^{\circ}$ d) $\alpha$ = $180^{\circ}$
3. Tìm góc $\alpha$ ($0^{\circ} \leq \alpha \leq 180^{\circ}$) trong mỗi trường hợp sau:
a) cos$\alpha$ = - $\frac{\sqrt{2}}{2}$; b) sin$\alpha$ = 0;
c) tan$\alpha$ = 1; d) cot$\alpha$ không xác định.
a) $\alpha$ = $135^{\circ}$ b) $\alpha$ = $0^{\circ}$ hoặc $\alpha$ = $180^{\circ}$
c) $\alpha$ = $45^{\circ}$ d) $\alpha$ = $180^{\circ}$