e ,
ON – ON′ = |d – 
a n⋅ˆ |
r
Fig 11 19
(a)
a
Z
X
Y
d
N’
P
O
π1
π2
N
Q
π1
(b)
P
X
Z
Y
O
d
N’
N
π2
a
© NCERT
not to be republished
THREE D IMENSIONAL G EOMETRY
491
which is the length of the perpendicular from a point to the given plane We may establish the similar results for (Fig 11