ko bt làm :Đ
\(xy+1=x+y\)
\(\Leftrightarrow xy-x-y+1=x\left(y-1\right)-\left(y-1\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(y-1\right)=0\Leftrightarrow\orbr{\begin{cases}x-1=0\\y-1=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=1\\y=1\end{cases}}\)
Vậy: x=1 hoặc y=1
x+y=xy+1
<=> x+y-xy-1=0
<=> (x-xy) -(1-y)=0
<=> x(1-y)-(1-y)=0
<=> (x-1)(1-y)=0
\(\Leftrightarrow\hept{\begin{cases}x-1=0\\1-y=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=1\\y=1\end{cases}}}\)
