## Oriented Area

Give a necessary and sufficient condition for the oriented area of the triangle $(0,0), (x_1, y_1), (x_2,y_2)$ to be positive?

Do we have to incorporate the equation $y_{1}x - x_{1}y = 0$? What if you had $(x_1, y_1), (x_2,y_2), (x_3,y_3)$?