Đáp án:
\(\left[ \begin{array}{l}
\tan a = \dfrac{4}{3}\\
\tan a = - \dfrac{4}{3}
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
Do:\sin a = \dfrac{4}{5}\\
{\sin ^2}a + {\cos ^2}a = 1\\
\to \dfrac{{16}}{{25}} + {\cos ^2}a = 1\\
\to {\cos ^2}a = \dfrac{9}{{25}}\\
\to \left[ \begin{array}{l}
\cos a = \dfrac{3}{5}\\
\cos a = - \dfrac{3}{5}
\end{array} \right.\\
\to \left[ \begin{array}{l}
\tan a = \dfrac{4}{3}\\
\tan a = - \dfrac{4}{3}
\end{array} \right.
\end{array}\)
