Đáp án:
a) (d) song song với y=-2x+5 nên:
$\begin{array}{l}
\left\{ \begin{array}{l}
m - 1 = - 2\\
- 3n + 6 \ne 5
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
m = - 1\\
n \ne \frac{1}{3}
\end{array} \right.\\
\Rightarrow \left( d \right):y = - 2x - 3n + 6\,di\,qua\,A\left( {2; - 1} \right)\\
\Rightarrow - 1 = - 2.2 - 3n + 6\\
\Rightarrow n = 1\left( {tm} \right)\\
Vay\,m = - 1;n = 1\\
b)\left( d \right)\,qua\,X\left( {1,5;0} \right);Y\left( {0;1} \right)\\
\Rightarrow \left\{ \begin{array}{l}
\left( {m - 1} \right).1,5 - 3n + 6 = 0\\
- 3n + 6 = 1
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
\left( {m - 1} \right).\frac{3}{2} + 1 = 0\\
n = \frac{5}{3}
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
m = \frac{1}{3}\\
n = \frac{5}{3}
\end{array} \right.
\end{array}$
