The question is to find the equation of a plane through three points.

P (1,2,-1)

Q (2,3,1)

R (3,-1,2)

vectors

PQ (1,1,2)

RQ (1,-4,1)

PR (2,-3,3)

How come PQ and PR are parallel, is RQ parallel as well? I'm following my textbook and it doesn't mention anything about it.

I can do the work, I'm just curious about RQ.

Edit: Solved.