Đáp án:
$\begin{array}{l}
a)y = mx - 3//y = - 3x\\
\Leftrightarrow \left\{ \begin{array}{l}
m = - 3\\
- 3 \ne 0\left( {tm} \right)
\end{array} \right.\\
Vậy\,m = - 3\\
b)x = 1 + \sqrt 3 ;y = \sqrt 3 \\
\Leftrightarrow \sqrt 3 = m.\left( {1 + \sqrt 3 } \right) - 3\\
\Leftrightarrow \sqrt 3 + 3 = m.\left( {1 + \sqrt 3 } \right)\\
\Leftrightarrow m = \dfrac{{\sqrt 3 + 3}}{{1 + \sqrt 3 }} = \dfrac{{\sqrt 3 \left( {1 + \sqrt 3 } \right)}}{{1 + \sqrt 3 }} = \sqrt 3 \\
Vậy\,m = \sqrt 3
\end{array}$
