11 7  Coplanarity of Two Lines
Let the given lines be
rr  = 
1
1
a
b
+λ
r
r (1)
and
rr  = 
2
2
a
b
+ µ
r
r (2)
The line (1) passes through the point, say A, with position vector 
1
ar and is parallel
to 
1b
r