a. \(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{1-2y}{3}\\4x-2y=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{1-2y}{3}\\2\cdot\dfrac{1-2y}{3}-2y=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{1-2y}{3}\\\dfrac{2-4y-6y}{3}=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{1-2y}{3}\\y=-\dfrac{1}{10}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{1-2\cdot\left(-\dfrac{1}{10}\right)}{3}\\y=-\dfrac{1}{10}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{2}{5}\\y=-\dfrac{1}{10}\end{matrix}\right.\)
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b: \(\Leftrightarrow\left\{{}\begin{matrix}2x+3y=5\\2x-4y=-16\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=3\\x=-2\end{matrix}\right.\)
c: \(\Leftrightarrow\left\{{}\begin{matrix}20x+12y=28\\20x+8y=32\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-1\\x=\dfrac{5}{2}\end{matrix}\right.\)
