` x^2 -2y^2= x y `
`to x^2 -2y^2- x y =0`
`to x^2 -y^2-y^2- x y =0`
`to (x -y)(x+y)-y(y+ x) =0`
`to (x+y)(x -2y) =0`
\(\to\left[ \begin{array}{l}x=-y\\x=2y\end{array} \right.\)
`text(nếu )x=-y`
`P=(-y-y)/(-y+y)to(\text(vô lí))`
`text(nếu )x=2y`
`P=(2y-y)/(2y+y)=y/(3y)=1/3`