6 2) If PQ
uuur
 is the shortest distance vector between
l1 and l2 , then it being perpendicular to both  1b
r
 and
2b
r
, the unit vector nˆ  along PQ
uuur
 would therefore be
ˆn =
1
2
1
2
|
|
b
b
b
b
×
×
r
r
r
r (3)
Then
PQ
uuur
 = d nˆ
where, d is the magnitude of the shortest distance vector