Cho cosα = -√5/3 với π < α < 3π/2 . Giá trị tanα là
\(\begin{array}{l}
{\rm{A}}{\rm{.}}\frac{{ - 4}}{{\sqrt 5 }}\\
{\rm{B}}{\rm{.}}\frac{2}{{\sqrt 5 }}\\
{\rm{C}}{\rm{. - }}\frac{2}{{\sqrt 5 }}\\
{\rm{D}}{\rm{. - }}\frac{3}{{\sqrt 5 }}
\end{array}\)
Vì \(\begin{array}{l}
\pi < a < \frac{3}{2} \Rightarrow \sin a < 0,\tan a > 0\\
\cos a = - \frac{{\sqrt 5 }}{3} \Rightarrow \sin a = - \frac{2}{3} \Rightarrow \tan a = \frac{2}{{\sqrt 5 }}
\end{array}\)
-- Mod Toán 10