Tính t a n α

C

Ta có:\[{\sin ^2}\alpha = 1 - {\cos ^2}\alpha = 1 - \frac{9}{{25}} = \frac{{16}}{{25}} \Leftrightarrow \sin \alpha = \pm \frac{4}{5}\]

Do \[0 < \alpha < \frac{\pi }{2}\] nên \[\sin \alpha > 0\]. Do đó\[\sin \alpha = \frac{4}{5} \Rightarrow \tan \alpha = \frac{{\sin \alpha }}{{\cos \alpha }} = \frac{4}{3}\].