Solution Comparing the given equations of the planes with the equations
A1 x + B1 y + C1 z + D1 = 0  and  A2 x + B2 y + C2 z + D2 = 0
We get
A1 = 3, B1 = – 6, C1 = 2
 A2 = 2, B2 = 2, C2 = – 2
cos θ =
(
)
(
)
2
2
2
2
2
2
3
2
( 6) (2)
(2) ( 2)
3
( 6)
( 2)
2
2
( 2)
×
+ −
+
−
+ −
+ −
+
+ −
=
10
5
5 3
21
7
2 3
7 3
−
=
=
×
Therefore,
θ = cos-1  5 3
21








11 9  Distance of a Point from a Plane
Vector form
Consider a point P with position vector ar  and a plane π 1 whose equation is
⋅rr nˆ
 = d (Fig 11 19) Consider a plane π2 through P parallel to the plane  π1