Đáp án:
\(\begin{array}{l}
a)\left\{ \begin{array}{l}
x = 2\\
y = 1
\end{array} \right.\\
c)\left\{ \begin{array}{l}
x = - 6\\
y = - \dfrac{5}{2}
\end{array} \right.\\
b)\left\{ \begin{array}{l}
x = 4\\
y = \dfrac{{40}}{3}
\end{array} \right.\\
d)\left\{ \begin{array}{l}
x = 11\\
y = 9
\end{array} \right.
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
a)\left\{ \begin{array}{l}
2x - 11y = - 7\\
10x + 11y = 31
\end{array} \right.\\
\to \left\{ \begin{array}{l}
12x = 31 - 7\\
y = \dfrac{{31 - 10x}}{{11}}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
12x = 24\\
y = \dfrac{{31 - 10x}}{{11}}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 2\\
y = \dfrac{{31 - 10.2}}{{11}}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 2\\
y = 1
\end{array} \right.\\
c)\left\{ \begin{array}{l}
xy - 2x + 14y - 28 = xy\\
xy + x - 4y - 4 = xy
\end{array} \right.\\
\to \left\{ \begin{array}{l}
- 2x + 14y = 28\\
x - 4y = 4
\end{array} \right.\\
\to \left\{ \begin{array}{l}
- 2x + 14y = 28\\
2x - 8y = 8
\end{array} \right.\\
\to \left\{ \begin{array}{l}
- 6x = 36\\
y = \dfrac{{x - 4}}{4}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = - 6\\
y = - \dfrac{5}{2}
\end{array} \right.\\
b)\left\{ \begin{array}{l}
4x + 7y = 16\\
4x - 3y = - 24
\end{array} \right.\\
\to \left\{ \begin{array}{l}
4x + 7y = 16\\
- 4x + 3y = 24
\end{array} \right.\\
\to \left\{ \begin{array}{l}
10x = 40\\
y = \dfrac{{4x + 24}}{3}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 4\\
y = \dfrac{{4.4 + 24}}{3}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 4\\
y = \dfrac{{40}}{3}
\end{array} \right.\\
d)\left\{ \begin{array}{l}
6x - 9x = - 15\\
- 6x + 8y = 4
\end{array} \right.\\
\to \left\{ \begin{array}{l}
- x = - 11\\
y = \dfrac{{6x + 15}}{9}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 11\\
y = \dfrac{{6.11 + 15}}{9}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 11\\
y = 9
\end{array} \right.
\end{array}\)