13 Show that the lines 
5
2
7
5
1
x
y
z
−
+
=
=
−
 and 
1
2
3
x
y
z
=
=
 are perpendicular to
each other 14 Find the shortest distance between the lines
ˆ
ˆ
ˆ
(
2
)
r
i
j
k
=
+
+
r
 + 
ˆ
ˆ
ˆ
(
)
i
j
k
λ
−
+
 and
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
2
(2
2 )
r
i
j
k
i
j
k
=
−
−
+ µ
+
+
r
15