Then
ˆn = 
ˆ
ˆ
ˆ
l i
m j
n k
+ +
X
Y
Z
N
P(
)
x, y,z
 r
d
O
Fig 11 10
© NCERT
not to be republished
 MATHEMATI CS
480
Therefore, (2) gives
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
(
) (
)
x i
y j
z k
l i
m j
n k
d
+
+
⋅
+
+
=
i e ,
 lx + my + nz = d