That is not what I said. This is what I said:

“1) Find PQ,PR,PS: two of these have to be adjacent sides of a quadrilateral.”

I obviously meant a space (non-planar) quadrilateral since we are talking about points in R3. quadri-four, lateral-side.

However, if that bothers you, Any two lines emanating from a point are sides of some (plane) quadrilateral(s): by elementary geometry.

Either one works.

I find it hard to believe that this has to be explained to you.