The center of the straight line moves in all five cases parallel to itself and creates the red envelope. |

The cyan end of the straight line moves along the magenta circle.
(The length of the line is 1.6 times the radius of the circle).
The green end yields the outer (black) curve. Rerun | |

The cyan and the green end of the chord move along
the outer (black) curve. Rerun | |

The cyan end of the straight line moves along the magenta circle.
(The length of the line is 1.6 times the radius of the circle).
The green end yields the inner (black) curve Rerun | |

The cyan and the green end of the chord move along
the inner (black) curve. Rerun | |

The cyan and the green end of the straight line move along
the inner (blue) and the outer (black) curve. Rerun |