Đáp án:

a. \(\left\{ \begin{array}{l}
x = \frac{1}{5}\\
y = \frac{2}{5}
\end{array} \right.\)

Giải thích các bước giải:

\(\begin{array}{l}
a.\left\{ \begin{array}{l}
2x + 4y = 2\\
3x - 4y =  - 1
\end{array} \right. \to \left\{ \begin{array}{l}
5x = 1\\
x + 2y = 1
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = \frac{1}{5}\\
y = \frac{2}{5}
\end{array} \right.\\
b.\left\{ \begin{array}{l}
x + 2y = 5\\
6x - 2y = 2
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
7x = 7\\
x + 2y = 5
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = 1\\
y = 2
\end{array} \right.\\
c.\left\{ \begin{array}{l}
3x = 3\\
x - 3y = 4
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = 1\\
y =  - 1
\end{array} \right.\\
d.\left\{ \begin{array}{l}
3x =  - 3\\
x + 3y =  - 2
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x =  - 1\\
y =  - \frac{1}{3}
\end{array} \right.\\
e.\left\{ \begin{array}{l}
3x - 4y = 10\\
 - 16x + 4y =  - 36
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
 - 13x =  - 26\\
4x - y = 9
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = 2\\
y =  - 1
\end{array} \right.\\
f.\left\{ \begin{array}{l}
3x = 3\\
x + 3y = 4
\end{array} \right. \to \left\{ \begin{array}{l}
x = 1\\
y = 1
\end{array} \right.\\
g.\left\{ \begin{array}{l}
5x + 2y = 4\\
4x - 2y = 14
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
9x = 18\\
2x - y = 7
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = 2\\
y =  - 3
\end{array} \right.
\end{array}\)