Đáp án:
$\begin{array}{l}
2)\pi < a < \dfrac{{3\pi }}{2}\\
\Rightarrow \cos a < 0\\
\Rightarrow \cos a = - \sqrt {1 - {{\sin }^2}a} = - \dfrac{{\sqrt {33} }}{7}\\
\Rightarrow \tan a = \dfrac{{\sin a}}{{\cos a}} = \dfrac{{4\sqrt {33} }}{{33}}\\
\cos 2a = 2{\cos ^2}a - 1 = \dfrac{{17}}{{49}}\\
3)\\
a)AB:y = a.x + b\\
\Rightarrow \left\{ \begin{array}{l}
- 5 = 3a + b\\
3 = a + b
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
a = - 4\\
b = 7
\end{array} \right.\\
\Rightarrow AB:y = - 4x + 7\\
TT:AC:y = - \dfrac{4}{5}x - \dfrac{{13}}{5}\\
b)CH \bot AB\\
\Rightarrow CH:y = \dfrac{1}{4}.x + b\left( {do:\dfrac{1}{4}.\left( { - 4} \right) = - 1} \right)\\
C \in CH\\
\Rightarrow - 1 = \dfrac{1}{4}.\left( { - 2} \right) + b\\
\Rightarrow b = - \dfrac{1}{2}\\
\Rightarrow CH:y = \dfrac{1}{4}x - \dfrac{1}{2}
\end{array}$
