Đáp án:
4) \(\left\{ \begin{array}{l}
x = 15\\
y = 10
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
1)\left\{ \begin{array}{l}
x = 5 - \dfrac{y}{3}\\
2\left( {5 - \dfrac{y}{3}} \right) - 5y = 10
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 5 - \dfrac{y}{3}\\
10 - \dfrac{2}{3}y - 5y = 10
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 5 - \dfrac{y}{3}\\
- \dfrac{{17}}{3}y = 0
\end{array} \right.\\
\to \left\{ \begin{array}{l}
y = 0\\
x = 5
\end{array} \right.\\
2)\left\{ \begin{array}{l}
x = \dfrac{{1 + 3y}}{4}\\
\dfrac{{2\left( {\dfrac{{1 + 3y}}{4}} \right) + 1}}{6} = \dfrac{{9 - 5y}}{8}\left( 1 \right)
\end{array} \right.\\
\left( 1 \right) \to \dfrac{{1 + 3y + 2}}{{24}} = \dfrac{{9 - 5y}}{8}\\
\to 3 + 3y = 27 - 15y\\
\to 18y = 24\\
\to y = \dfrac{4}{3} \to x = \dfrac{5}{4}\\
3)\left\{ \begin{array}{l}
y = 5x - 11\\
\dfrac{1}{3}x + \dfrac{1}{4}.\left( {5x - 11} \right) - 2 = 0\left( 1 \right)
\end{array} \right.\\
\left( 1 \right) \to \dfrac{{19}}{{12}}x - \dfrac{{11}}{4} - 2 = 0\\
\to x = - 3\\
\to y = - 26\\
4)\left\{ \begin{array}{l}
4x - 5y = 10\\
3x - 5y = - 5
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 15\\
4x - 5y = 10
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 15\\
y = 10
\end{array} \right.
\end{array}\)
