Question

giải phương trình sau bằng phương pháp thế

Answer 1

\(\left\{{}\begin{matrix}x+y=-2\left(x-1\right)\\7x+3y=x+y+5\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x+y=-2x+2\\7x+3y-x-y=5\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x+y+2x=2\\6x+2y=5\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}3x+y=2\\6x+2y=5\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}3x+y=2\\2\left(3x+y\right)=5\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}3x+y=2\\3x+y=\dfrac{5}{2}\end{matrix}\right.\)

Mà: \(2\ne\dfrac{5}{2}\) => Hpt vô nghiệm