Inscribing a quadrilateral in a circle

  • Thread starter Thread starter ehrenfest
  • Start date Start date
  • Tags Tags
    Circle
Click For Summary

Homework Help Overview

The discussion revolves around the conditions under which a quadrilateral can be inscribed in a circle, particularly focusing on the relationship between the angles of the quadrilateral. The original poster questions whether having both pairs of opposite angles summing to 180 degrees guarantees that the quadrilateral can be inscribed in a circle.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the implications of the angle properties of quadrilaterals and whether these properties are sufficient for inscribing the shape in a circle. Some participants question the necessity of all four vertices being on the circle, while others discuss the conditions under which certain points can lie on the circle.

Discussion Status

The discussion is ongoing, with various interpretations being explored regarding the inscribing condition. Some participants provide insights into the properties of angles and circles, while others express skepticism about the original claim. There is no explicit consensus yet, but several lines of reasoning are being examined.

Contextual Notes

Participants note that the properties of angles in quadrilaterals may not always lead to the conclusion that all vertices can be inscribed in a circle, indicating a need for further exploration of the definitions and assumptions involved.

ehrenfest
Messages
2,001
Reaction score
1

Homework Statement



If both pairs of opposite angles of a quadrilateral add up to 180, is it always possible to inscribe it in a circle?


Homework Equations





The Attempt at a Solution



The converse is easily proven, since the angle between two chords standing on the circumfrence is half of the corresponding central angle.
 
Physics news on Phys.org
If by inscribe, you mean that all four vertices lie on the circle, I don't think so.
 
chaoseverlasting said:
If by inscribe, you mean that all four vertices lie on the circle, I don't think so.

It is true. Draw the circle containing three points of the quadrilateral and then use the supplementary angle property to show the fourth point must lie on the circle.
 
Yes, but if only two points lie on the circle, then the other two don't necessarily have to. Thats what I was thinking about. The same obviously goes for one point lying on the circle.

In any case, the opposite angles of a quadrilateral will always be supplementary.
 
chaoseverlasting said:
In any case, the opposite angles of a quadrilateral will always be supplementary.

No, e.g. a diamond.
 
chaoseverlasting said:
Yes, but if only two points lie on the circle, then the other two don't necessarily have to. Thats what I was thinking about. The same obviously goes for one point lying on the circle.

In any case, the opposite angles of a quadrilateral will always be supplementary.

You can put a circle through any three noncollinear points.
 

Similar threads

  • · Replies 52 ·
2
Replies
52
Views
4K
Replies
1
Views
3K
  • · Replies 9 ·
Replies
9
Views
4K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 24 ·
Replies
24
Views
7K
  • · Replies 30 ·
2
Replies
30
Views
6K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 13 ·
Replies
13
Views
10K
  • · Replies 48 ·
2
Replies
48
Views
6K
  • · Replies 11 ·
Replies
11
Views
3K