Cord Separates the Unit Disc.

Normal Vector:
\[
   \underline{n}=
   \widehat{ \underline{e}_Q-\underline{e}_P  }
   =
   \underline{f}_Q-\underline{f}_P
   =
   \begin{pmatrix}
     \sin{\theta_P}-\sin{\theta_Q}\\cos{\theta_Q}-\cos{\theta_P}
   \end{pmatrix}
\]

Equation:

\[
   (\sin{\theta_P}-\sin{\theta_Q})(x-\cos{\theta_P})
   +
   (\cos{\theta_Q}-\cos{\theta_P})(y-\sin{\theta_P})
   =
   0
\]
Or:
\[
   (\sin{\theta_P}-\sin{\theta_Q})x
   +
   (\cos{\theta_Q}-\cos{\theta_P})y
   =
\]
\[
   (\sin{\theta_P}-\sin{\theta_Q})\cos{\theta_P}
   +
   (\cos{\theta_Q}-\cos{\theta_P})\sin{\theta_P}
   =
\]
\[
   \sin{\theta_Q}\cos{\theta_P}
   +
   \cos{\theta_Q}\sin{\theta_P}
   =
\]
\[
   \sin{(\theta_Q+\theta_P)}
\]
Thus:

\[
   (\sin{\theta_P}-\sin{\theta_Q})x
   +
   (\cos{\theta_Q}-\cos{\theta_P})y
   =
   \sin{(\theta_Q+\theta_P)}
\]

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   @Image Klein.Separation.svg height=100px
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