Đáp án:

$\begin{array}{l}
1)a)\dfrac{x}{3} = \dfrac{{ - 2}}{y}\\
 \Rightarrow x.y = 3.\left( { - 2} \right) =  - 6 = \left( { - 1} \right).6\\
x > 0 > y\\
 \Rightarrow \left[ \begin{array}{l}
x = 3;y =  - 2\\
x = 2;y =  - 3\\
x = 1;y =  - 6\\
x = 6;y =  - 1
\end{array} \right.\\
b)\dfrac{5}{y} = \dfrac{x}{{ - 2}}\\
 \Rightarrow x.y = 5.\left( { - 2} \right) = 10 = 1.\left( { - 10} \right)\\
y < 0 < x\\
 \Rightarrow \left[ \begin{array}{l}
x = 5;y =  - 2\\
x = 2;y =  - 5\\
x = 1;y =  - 10\\
x = 10;y =  - 1
\end{array} \right.\\
c)\dfrac{{x - 3}}{{y - 2}} = \dfrac{3}{2}\\
 \Rightarrow 3.\left( {y - 2} \right) = 2.\left( {x - 3} \right)\\
 \Rightarrow 3.y - 3.2 = 2.x - 2.3\\
 \Rightarrow 3.y - 6 = 2.x - 6\\
 \Rightarrow 3.y = 2.x\\
 \Rightarrow y = \dfrac{2}{3}.x\\
Do:x - y = 4\\
 \Rightarrow x - \dfrac{2}{3}.x = 4\\
 \Rightarrow \dfrac{1}{3}.x = 4 \Rightarrow x = 4.3 = 12\\
 \Rightarrow y = \dfrac{2}{3}.x = \dfrac{2}{3}.12 = 8\\
Vay\,x = 12;y = 8\\
C2)a)16 = {2^4}\\
72 = {2^3}{.3^2}\\
 \Rightarrow MSC = {2^4}{.3^2} = 144\\
 \Rightarrow \left\{ \begin{array}{l}
\dfrac{{ - 5}}{{16}} = \dfrac{{ - 5.9}}{{144}} = \dfrac{{ - 45}}{{144}}\\
\dfrac{{33}}{{ - 72}} = \dfrac{{ - 33.2}}{{72.2}} = \dfrac{{ - 66}}{{144}}
\end{array} \right.\\
b)56 = {2^3}.7;63 = {3^2}.7;144 = {2^4}{.3^2}\\
 \Rightarrow MSC = {2^4}{.3^2}.7 = 1008\\
 \Rightarrow \left\{ \begin{array}{l}
\dfrac{{ - 1}}{{56}} = \dfrac{{ - {{2.3}^2}}}{{1008}} = \dfrac{{ - 18}}{{1008}}\\
\dfrac{{ - 11}}{{ - 63}} = \dfrac{{11.16}}{{1008}} = \dfrac{{176}}{{1008}}\\
\dfrac{{26}}{{144}} = \dfrac{{26.7}}{{1008}} = \dfrac{{182}}{{1008}}
\end{array} \right.\\
c)24 = {2^3}.3;15 = 3.5;40 = {2^3}.5\\
 \Rightarrow MSC = {2^3}.3.5 = 120\\
 \Rightarrow \left\{ \begin{array}{l}
\dfrac{{ - 7}}{{24}} = \dfrac{{ - 7.5}}{{120}} = \dfrac{{ - 35}}{{120}}\\
\dfrac{{14}}{{15}} = \dfrac{{14.8}}{{120}} = \dfrac{{112}}{{120}}\\
\dfrac{{ - 3}}{{40}} = \dfrac{{ - 3.3}}{{120}} = \dfrac{{ - 9}}{{120}}
\end{array} \right.
\end{array}$