Найдите tg 𝛼 ${\displaystyle \mathrm{tg}\alpha }$ , если sin 𝛼 = − 2 5 ‾ √ ${\displaystyle \sin \alpha =-\frac{2}{\sqrt{5}}}$ и 180 ° < 𝛼 < 270 ° ${\displaystyle 180°<\alpha <270°}$ .