Giải thích các bước giải:
3)
\(\begin{array}{l}
3)\left\{ \begin{array}{l}
x + y = 2\\
mx - y = 1
\end{array} \right.\\
a)m = 1 \Rightarrow \left\{ \begin{array}{l}
x + y = 2\\
x - y = 1
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
2x = 3\\
y = 2 - x
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x = \dfrac{3}{2}\\
y = \dfrac{1}{2}
\end{array} \right.\\
b)\left\{ \begin{array}{l}
x + y = 2\\
mx - y = 1
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
\left( {m + 1} \right)x = 3\\
y = 2 - x
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
x = \dfrac{3}{{m + 1}}\left( {m \ne - 1} \right)\\
y = 2 - \dfrac{3}{{m + 1}}
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
x = \dfrac{3}{{m + 1}}\\
y = \dfrac{{2m - 1}}{{m + 1}}
\end{array} \right.\\
Vi\left\{ \begin{array}{l}
x + y = 2 > 0\\
xy > 0\left( {gt} \right)
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
x > 0\\
y > 0
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
\dfrac{3}{{m + 1}} > 0\\
\dfrac{{2m - 1}}{{m + 1}} > 0
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
m + 1 > 0\\
2m - 1 > 0
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
m > - 1\\
m > \dfrac{1}{2}
\end{array} \right. \Leftrightarrow m > \dfrac{1}{2}
\end{array}\)
Em tách ra hỏi từng câu thôi nhé
