Question

Giải hệ phương trình sau bằng cách cộng hệ số 

 1) \(\left\{{}\begin{matrix}x-y=5\\2x+y=11\end{matrix}\right.\)

2) \(\left\{{}\begin{matrix}3x+2y=1\\3x+y=2\end{matrix}\right.\)

3) \(\left\{{}\begin{matrix}x-y=2\\3x+2y=11\end{matrix}\right.\)

Answer 1

\(1,\Leftrightarrow\left\{{}\begin{matrix}x=y+5\\2y+10+y=11\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{16}{3}\\y=\dfrac{1}{3}\end{matrix}\right.\\ 2,\Leftrightarrow\left\{{}\begin{matrix}3x=1-2y\\1-2y+y=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1\\y=-1\end{matrix}\right.\\ 3,\Leftrightarrow\left\{{}\begin{matrix}x=y+2\\3y+6+2y=11\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=3\\y=1\end{matrix}\right.\)