2. Given a plane and a point not on it, $\Pi :\,\,N \cdot (R - P) = 0\,\& \,Q \notin \Pi$.
Then the distance between the two is: $D(\Pi ;Q) = \frac{{\left| {\overrightarrow {PQ} \cdot N} \right|}}{{\left\| N \right\|}}$