$\text{a)}$  

$\mathrm{tg}\alpha =-\sqrt{3}$  

$\mathrm{tg}\alpha =-\mathrm{tg}{60}^{\circ }$     

$\mathrm{tg}\alpha =\mathrm{tg}\left({180}^{\circ }-{60}^{\circ }\right)$  

$\alpha ={120}^{\circ }$  

---

$\text{b)}$  

$\mathrm{tg}\alpha =0$  

$\mathrm{tg}\alpha =\mathrm{tg}{0}^{\circ }$  

$\alpha =0^{\circ }$  

---

$\text{c)}$  

$\mathrm{tg}\alpha =\frac{1}{\sqrt{3}}$  

$\mathrm{tg}\alpha =\frac{\sqrt{3}}{3}$  

$\mathrm{tg}\alpha =\mathrm{tg}{30}^{\circ }$  

$\alpha ={30}^{\circ }$  

---

$\text{d)}$  

$\mathrm{tg}\alpha =-1$  

$\mathrm{tg}\alpha =-\mathrm{tg}{45}^{\circ }$  

$\mathrm{tg}\alpha =\mathrm{tg}\left({180}^{\circ }-{45}^{\circ }\right)$  

$\alpha ={135}^{\circ }$