$\left\{\begin{matrix}3(x+1)+2(x+2y)=4\\4(x+1)-(x+2y)=9\end{matrix}\right.$
`<=>`$\left\{\begin{matrix}3x+3+2x+4y=4\\4x+4-x-2y=9\end{matrix}\right.$
`<=>`$\left\{\begin{matrix}5x+4y=1\\3x-2y=5\end{matrix}\right.$`<=>`$\left\{\begin{matrix}5x+4y=1\\6x-4y=10\end{matrix}\right.$
`<=>`$\left\{\begin{matrix}11x=11\\y=\dfrac{3x-5}2\end{matrix}\right.$`<=>`$\left\{\begin{matrix}x=1\\y=-1\end{matrix}\right.$
Vậy hệ phương trình có nghiệm duy nhất $(x;y)=(1;-1)$
