14
The vectors RS
uuur
 and RT
uuur
 are in the given plane Therefore, the vector RS
RT
×
uuur
uuur
is perpendicular to the plane containing points R, S and T Let rr be the position vector
of any point P in the plane Therefore, the equation of the plane passing through R and
perpendicular to the vector RS
RT
×
uuur
uuur
 is
(
) (RS
RT)
r
−a
⋅
×
uuur
uuur
r
r
 = 0
or
r
r
r
r
r
r
(
)