Corresponding angles on parallel lines.
As you move the points, what do you notice about the [color=#38761d]green[/color] angles?
As you move the points, what do you notice about the [color=#ff7700]orange[/color] angles?
As you move the points, what do you notice about the [color=#9900ff]purple[/color] angles?
As you move the points, what do you notice about the [color=#0000ff]blue[/color] angles?