Cho sin alpha = 1/3(pi/2

Ta có:

${\cos }^2\alpha =1-{\sin }^2\alpha$

$\Rightarrow {\cos }^2\alpha =\frac{8}{9}$

$\Rightarrow \cos \alpha =\pm \frac{2\sqrt{2}}{3}$

Vì $\frac{\pi }{2}<\alpha <\pi \Rightarrow$$\cos \alpha =\frac{-2\sqrt{2}}{3}$

$\Rightarrow \tan \alpha =\frac{\sin \alpha }{\cos \alpha }=\frac{-\sqrt{2}}{4}$