Bài tập 31 trang 206 SGK Toán 10 NC

Do 180⁰ < 250⁰ < 270⁰ nên cos 250⁰ < 0 

\(\begin{array}{*{20}{l}}
\begin{array}{l}
*\tan \left( { - {{672}^0}} \right) =  - \tan {672^0}\\
 =  - \tan \left( { - {{48}^0} + {{2.360}^0}} \right)\\
 = \tan {48^0} > 0
\end{array}\\
\begin{array}{l}
*\tan \frac{{31\pi }}{8} = \tan \left( { - \frac{\pi }{8} + 4\pi } \right)\\
 = \tan \left( { - \frac{\pi }{8}} \right) =  - \tan \frac{\pi }{8} < 0
\end{array}\\
\begin{array}{l}
*\sin \left( { - {{1050}^0}} \right) = \sin \left( {{{30}^0} - {{3.360}^0}} \right)\\
 = \sin {30^0} = \frac{1}{2} > 0
\end{array}\\
\begin{array}{l}
*\cos \frac{{16\pi }}{5} = \cos \left( {3\pi  - \frac{\pi }{5}} \right)\\
 =  - \cos \frac{\pi }{5} < 0
\end{array}
\end{array}\)

-- Mod Toán 10 HỌC247