Your friend drew the diagram to prove to you that two planes can intersect in exactly one point. Describe your friend's error. How do you describe a plane? What does it mean for two planes to intersect each other and what are possible intersections of two planes? Can you define an endpoint of a plane?
If two planes intersect, they intersect in a line. The line and the plane intersect in a single point. The line and the plane do not interesect. In this case they are called parallel.
