Find the position vector of the mid point of the vector joining the points  P(2, 3, 4)
and Q(4, 1, –2) 17 Show that the points A, B and C with position vectors, 
ˆ
ˆ
ˆ
3
4
4 ,
a
i
j
k
=
−
−
r
ˆ
ˆ
ˆ
2
b
i
j
k
=
−
+
r
 and 
ˆ
ˆ
3ˆ
5
c
i
j
k
= −
−
r
, respectively form the vertices of a right angled
triangle 18