Formula
$$\begin{vmatrix} x&y&1\\x_1&y_1&1 \\ x_2&y_2&1 \end{vmatrix} = 0$$
Variables
A(x1, y1)
→
Point on a line
B(x2, y2)
→
Point on a line
$$\begin{vmatrix} x&y&1\\x_1&y_1&1 \\ x_2&y_2&1 \end{vmatrix} = 0$$