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
(
) [(
)×(
)]
r –a
b –a
c –a
 = 0                                                       … (1)
© NCERT
not to be republished
 MATHEMATI CS
484
Fig 11