Ta có : \(\left\{{}\begin{matrix}5-4y=20\\\frac{x}{4}-\frac{y}{5}=1\end{matrix}\right.\)
=> \(\left\{{}\begin{matrix}y=-\frac{15}{4}\\\frac{x}{4}-\frac{-\frac{15}{4}}{5}=1\end{matrix}\right.\)
=> \(\left\{{}\begin{matrix}y=-\frac{15}{4}\\\frac{x}{4}=\frac{7}{4}\end{matrix}\right.\)
=> \(\left\{{}\begin{matrix}y=-\frac{15}{4}\\x=7\end{matrix}\right.\)
Vậy phương trình có nghiệm là \(\left(x,y\right)=\left(7,-\frac{15}{4}\right)\)