p
o
l
a
r
c
u
r
v
e
a
c
o
s
(
b
θ
)
a
s
i
n
(
b
θ
)
a
+
b
c
o
s
(
θ
)
a
+
b
s
i
n
(
θ
)
a
-
b
c
o
s
(
θ
)
a
-
b
s
i
n
(
θ
)
a
2
b
3