a) \(xy=x+y\Rightarrow y=xy-x=x\left(y-1\right)\)
\(\Rightarrow x:y=\frac{x}{x\left(y-1\right)}=y-1\)
\(\Rightarrow x+y=y-1\Leftrightarrow x=-1\)
\(\Rightarrow y-1=-y\Leftrightarrow2y=1\Leftrightarrow y=\frac{1}{2}\)
Vậy \(x=-1;y=\frac{1}{2}\)
b) \(x-y=xy\Rightarrow x=xy+y=y\left(x+1\right)\)
\(\Rightarrow x:y=\frac{y\left(x+1\right)}{y}=x+1\)
\(\Rightarrow x-y=x+1\Leftrightarrow y=-1\)
\(\Leftrightarrow x+1=-x\Leftrightarrow2x=-1\Leftrightarrow x=\frac{-1}{2}\)