Vì x,y tlt nên \(\dfrac{x_1}{y_1}=\dfrac{x_2}{y_2}\)
Áp dụng tc dtsbn:
\(\dfrac{x_1}{y_1}=\dfrac{x_2}{y_2}=\dfrac{x_1-x_2}{y_1-y_2}=\dfrac{2}{-1}=-2\\ \Rightarrow\left\{{}\begin{matrix}y_1=-\dfrac{x_1}{2}\\y_2=-\dfrac{x_2}{2}\end{matrix}\right.\)
Vậy \(y=-\dfrac{x}{2}\)



