Show that two different parallel lines are either projected onto parallel lines or on two points by a projection $p_{π,d}$ , where $π : Ax + By + Cz + D = 0, d : \frac{x − x_0} p =\frac{y − y_0} q= \frac{z − z_0}r$ and $π\nparallel d$.
Can somebody help me with this problem, please? I have no idea how to start it even.