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WillemienH (talk | contribs) →Proof in the Klein model: renamed, layout improvement, but also found error in proof |
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* If both chords are diameters, they intersect.(at the center of the boundary circle)
* If only one of the chords is a diameter, the other chord projects orthogonally down to a section of the first chord contained in its interior, and a line from the pole orthogonal to the diameter intersects both the diameter and the chord.
* If both lines are not diameters, then we may extend the tangents drawn from each pole to produce a [[quadrilateral]] with the unit circle inscribed within it.{{how|date=August 2015}} The poles are opposite vertices of this quadrilateral, and the chords are lines drawn between adjacent sides of the vertex, across opposite corners. Since the quadrilateral is convex, the line between the poles intersects both of the chords drawn across the corners, and the segment of the line between the chords defines the required chord perpendicular to the two other chords.{{how|date=August 2015}}
<!-- ??? "then we may extend the tangents drawn from each pole to produce a [[quadrilateral]] with the unit circle inscribed within it " this is not always the case , they not always form a quadrilateral -->
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