\(\Leftrightarrow\left\{{}\begin{matrix}-2x-2y=5\\2x-2y=12\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-4y=17\\x-y=6\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{17}{4}\\x=6+y=\dfrac{-17}{4}+6=\dfrac{7}{4}\end{matrix}\right.\)
\(\left\{{}\begin{matrix}-2x-2y=5\\x-y=6\end{matrix}\right.\)(1)
(1) \(\Rightarrow\)\(\left\{{}\begin{matrix}-2x-2y=5\\2x-2y=12\end{matrix}\right.\)
cộng từng vế của 2 phương trình ta đc:
(1) \(\Rightarrow\)-4y=17
(1)\(\Rightarrow\)\(\left\{{}\begin{matrix}-4y=17\\x-y=6\end{matrix}\right.\)\(\Leftrightarrow\)\(\left\{{}\begin{matrix}y=\dfrac{-17}{4}\\x+\dfrac{17}{4}=6\end{matrix}\right.\)\(\Leftrightarrow\)\(\left\{{}\begin{matrix}y=\dfrac{-17}{4}\\x=6-\dfrac{17}{4}\end{matrix}\right.\)\(\Leftrightarrow\)\(\left\{{}\begin{matrix}y=\dfrac{-17}{4}\\x=\dfrac{7}{4}\end{matrix}\right.\)
