Then a
+b
r
r
is a unit vector if
(A)
θ =π4
(B)
θ =π3
(C)
θ =π2
(D)
π32
θ =
18 The value of 
ˆ
ˆ
ˆ
ˆ ˆ
ˆ
ˆ
ˆ
ˆ (
)
(
)
(
)
i
j
k
j
i
k
k
i
j
 
 
 
 
 
 
 
 is
(A) 0
(B) –1
(C) 1
(D) 3
19 If θ is the angle between any two vectors   and 
a
rb
r
, then |
| |
|
a b
a b
⋅
=
×
r
r
r
r
 when
θ is equal to
(A) 0
(B)
π4
(C)
π2
(D) π
Summary
� Position vector of a point P(x, y, z) is given as 
ˆ
ˆ
ˆ
OP(
r)
xi
yj
zk
=
=
+
+
uuur
r
, and its
magnitude by 
2
2
2
x
y
z
+
+