Talk:Ex-tangential quadrilateral

Clarification requested[edit]

The lede says "an ex-tangential quadrilateral is a convex quadrilateral where the extensions of all four sides are tangent to a circle outside the quadrilateral", and a rhombus is said to be a special case. I can't get this to happen with a rhombus -- could you clarify this?

Also, I hope you can provide an image of one of these with its excircle. Duoduoduo (talk) 23:05, 18 August 2011 (UTC)[reply]

The image is added. It shows an arbitarary ex-tangential quadrilateral, but it is not difficult now to imagine the excircle for a rhombus. Circlesareround (talk) 15:33, 19 August 2011 (UTC)[reply]

Thank you Duoduoduo for fixing the text. I see now how stupid my remark above was. I probably was thinking about kites but wrote rhombus, which was the issue. Circlesareround (talk) 16:58, 19 August 2011 (UTC)[reply]

Clarification needed[edit]

The lede currently says

The excenter lies at the intersection of the angle bisectors to the exterior angles at the extensions of the sides and the sides extended.

I don't understand this wording -- can it be clarified? Thanks. Duoduoduo (talk) 19:18, 1 April 2013 (UTC)[reply]

Meaning of "external angle bisector"[edit]

The passage in the lede cited above refers to the external angles' bisectors, and the second sentence of the section "Characterizations" also refers to "external angle bisectors". In both cases what I think is meant is the bisector of the angle supplementary to the interior angle. But the article Angle bisector says

The interior bisector of an angle is the half-line or line segment that divides an angle of less than 180° into two equal angles. The exterior bisector is the half-line that divides the opposite angle (of greater than 180°) into two equal angles.

Are both of these definitions widely accepted? I wonder if confusion is created by using this term in this way here. Duoduoduo (talk) 19:25, 1 April 2013 (UTC)[reply]

External angle = exterior angle (see external angle) and these are the ones you quote above. Circlesareround (talk) 17:58, 2 April 2013 (UTC)[reply]

So, what about the quote I gave above in italics from the article Angle bisector -- is that an alternative accepted usage, or should it be changed to coincide with the usage in this article (which I see agrees with Mathworld's usage)? Duoduoduo (talk) 20:08, 2 April 2013 (UTC)[reply]

I think that even Mathworld uses the term "exterior angle" in two different ways. From Exterior angle :

An exterior angle beta of a polygon is the angle formed externally between two adjacent sides. It is therefore equal to 2pi-alpha....

But from Exterior angle bisector :

The exterior angle bisectors (Johnson 1929, p. 149), also called the external angle bisectors (Kimberling 1998, pp. 18-19), of a triangle DeltaABC are the lines bisecting the angles formed by the sides of the triangles and their extensions, as illustrated above. Note that the exterior angle bisectors therefore bisect the supplementary angles of the interior angles, not the entire exterior angles.

Duoduoduo (talk) 21:14, 2 April 2013 (UTC)[reply]

OK, now I see what you mean. The definition of Exterior angle from Mathworld where it is 2pi - interior angle is, as far as I know, a very rare definition. If you make a picture search at Google you see that Exterior angle is (almost) always defined to be the angle between a side and the extension of an adjacent side. This is also the definition jused here at Wikipedia in this article as well as in the articles on angle bisectors (Internal and external angle and Bisection). So there is no problem, or? There is no inconsistance here anyway. Circlesareround (talk) 17:03, 3 April 2013 (UTC)[reply]

I think everything is fine now. Yesterday after I left my last comment here I changed the definition of external angle bisector at Bisection to agree with you.