Câu 2
$a)\,\,\overrightarrow {AB} = \left( { - 3;\,\, - 4} \right)\,\,;\,\,\,\,\,\,\,\,\,\,\,\overrightarrow {AC} = \left( {4;\,\, - 3} \right)$
b)
\(\begin{array}{l}
D\left( {x;0} \right) \in Ox\\
\overrightarrow {AD} = \left( {x - 2; - 3} \right)\\
\overrightarrow {AB} = \left( { - 3; - 4} \right)\\
gt \Rightarrow \dfrac{{x - 2}}{{ - 3}} = \dfrac{{ - 3}}{{ - 4}}\\
\Rightarrow 4x - 8 = - 9\\
\Leftrightarrow x = - \dfrac{1}{4} \Rightarrow D\left( { - \dfrac{1}{4};0} \right)
\end{array}\)