So, we may write the vector rr as
(
OP)
r =
uuur
r
=
ˆ
ˆ
cos
sin
i
j (1)
Clearly,
|
|
rr  =
2
2
cos
sin
1
θ +
θ =
Fig 10 28
Also, as θ varies from 0 to 2π, the point P (Fig 10 28) traces the circle x2 + y2 = 1
counterclockwise, and this covers all possible directions