Giải hệ phương trình \(\left\{{}\begin{matrix}\dfrac{x}{2}+\dfrac{y}{6}=-1\\2x+5y=-9\end{matrix}\right.\) bằng phương pháp thế, ta được nghiệm là
\(\left(x,y\right)=\left(-\dfrac{21}{13};-\dfrac{15}{13}\right)\).\(\left(x,y\right)=\left(-\dfrac{25}{13};-\dfrac{10}{13}\right)\).\(\left(x,y\right)=\left(-\dfrac{30}{17};-\dfrac{6}{17}\right)\).\(\left(x,y\right)=\left(-\dfrac{15}{17};-\dfrac{12}{17}\right)\).Hướng dẫn giải:\(\left\{{}\begin{matrix}\dfrac{x}{2}+\dfrac{y}{6}=-1\\2x+5y=-9\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}3x+y=-6\\2x+5y=-9\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=-6-3x\\2x+5\left(-6-3x\right)=-9\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=-6-3x\\-13x=21\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=-6-3x\\x=-\dfrac{21}{13}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=-\dfrac{21}{13}\\y=-\dfrac{15}{13}\end{matrix}\right.\)
