D = θ 1 - ϕ 1 + θ 2 - ϕ 2 1 2
D
=
θ
1
-
ϕ
1
+
θ
2
-
ϕ
2
1
2
D
=
θ
1
-
ϕ
1
+
θ
2
-
ϕ
2
1
2
