If the equation of the plane π2 is in the form 
rN
⋅ =d
rur
, where N
ur
 is normal
to the plane, then the perpendicular distance is |
N
|
| N |
a
⋅ −d
ur
r
ur 2 The length of the perpendicular from origin O to the plane 
rrurN⋅ =
d  is |
|
| N |
dur
(since ar  = 0) Cartesian form
Let P(x1, y1, z1) be the given point with position vector ar and
Ax + By + Cz = D
be the Cartesian equation of the given plane