Giải hệ phương trình bằng phương pháp thế
1) \(\left\{{}\begin{matrix}3x+y=1\\9x+3y=3\end{matrix}\right.\)
2) \(\left\{{}\begin{matrix}2x+y=10\\5x-3y=3\end{matrix}\right.\)
3) \(\left\{{}\begin{matrix}4x+y=2\\8x+3y=5\end{matrix}\right.\)
4) \(\left\{{}\begin{matrix}x-2y=1\\3x+5y=22\end{matrix}\right.\)
5 ) \(\left\{{}\begin{matrix}2x+y=-8\\-x+y=2\end{matrix}\right.\)
\(1,\Leftrightarrow\left\{{}\begin{matrix}3x+y=1\\3x+y=1\end{matrix}\right.\Leftrightarrow x,y\in R\\ 2,\Leftrightarrow\left\{{}\begin{matrix}y=10-2x\\5x+6x-30=3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=3\\y=10-2\cdot3=4\end{matrix}\right.\\ 3,\Leftrightarrow\left\{{}\begin{matrix}y=2-4x\\8x+6-12x=5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{1}{4}\\y=2-4\cdot\dfrac{1}{4}=1\end{matrix}\right.\\ 4,\Leftrightarrow\left\{{}\begin{matrix}x=1+2y\\3+6y+5y=22\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1+2y\\y=\dfrac{19}{11}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1+2\cdot\dfrac{19}{11}=\dfrac{49}{11}\\y=\dfrac{19}{11}\end{matrix}\right.\\ 5,\Leftrightarrow\left\{{}\begin{matrix}2x+x+2=-8\\y=x+2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-\dfrac{10}{3}\\y=-\dfrac{4}{3}\end{matrix}\right.\)
