- #1
hachi_roku
- 61
- 0
Homework Statement
show that three points P,Q, and R are collinear if and only if vec PQ x vec PR = 0
Homework Equations
The Attempt at a Solution
i understand this (i can see this visually in my head) but i just don't know how to say it mathematically...i know that the angle between them must be 0 or 180, but how do i show this?