Find the values of p so that the lines 1
7
14
3
3
2
2
x
y
z
p
−
−
−
=
=
and  7
7
5
6
3
1
5
x
y
z
p
−
−
−
=
=
 are at right angles 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