Proving PQ, PR, T, S, R and Q are Concyclic

  • Context: Undergrad 
  • Thread starter Thread starter Physics is Phun
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around proving that points T, S, R, and Q are concyclic given that PQ and PR are chords of a circle with center O, and OT is perpendicular to PQ while OS is perpendicular to PR, with OT equal to OS. Participants explore various approaches to the proof, including geometric properties and congruence of triangles.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant shares their proof steps but questions whether there is a simpler method, indicating they proved QT = RS and congruence of triangles QTO and RSO.
  • Another participant expresses doubt about the validity of the proof, noting an assumption that O is on QR, which may not be the case.
  • A third participant points out that T and S need clearer definitions for the proof to proceed effectively.
  • A later reply proposes that if T lies on PQ and S lies on PR, then certain equalities (PS = SR and PT = TQ) simplify the situation.
  • This participant discusses the properties of chords and perpendiculars in circles, suggesting that the right triangles OPS and OPT are congruent due to equal lengths OT and OS, leading to further congruences among triangles OPS, ORS, OPT, and OQT.
  • They also introduce the idea of proving that the perpendicular bisectors of RS, RQ, and QT intersect at a common point K, which would be the center of the circle containing T, S, R, and Q.
  • Symmetry about line OP is mentioned as a potential simplification for the proof.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the proof's validity or the best approach. There are competing views on the assumptions made and the clarity of definitions regarding points T and S.

Contextual Notes

Some assumptions regarding the positions of points T and S are not fully defined, which may affect the proof's validity. The discussion includes various mathematical steps and properties that are not resolved.

Physics is Phun
Messages
100
Reaction score
0
I finished this proof that took about a whole page and I was just wondering if there were an easier way of doing things that would take less work. here's the problem.
PQ and PR are two chords of a circle with centre O. OT is perpendicular to PQ and OS is perpendicular to PR. IF OT = OS prove that T,S,R and Q are concyclic.
I am going to go through my steps without proof cause it would take forever. I just want to get an idea if I am doing it the easiest way.

It would probably help if you drew this out.

First I proved QT = RS
then QTO is congruent to RSO
Then you can prove TS is parallel to QR
from there i can conclude that <QSR = <QTR
from there can I conlude that they are concyclic by equal angles in a segment?

Edit: I realized that I didn't need to prove parallel lines. It really doesn't help the question in any way.
 
Mathematics news on Phys.org
Ya, as I look at it, I don't think this proof works. I think I assumed O was on QR which it doesn't have to be. Now I really need help !
 
Physics is Phun said:
...
PQ and PR are two chords of a circle with centre O. OT is perpendicular to PQ and OS is perpendicular to PR. IF OT = OS prove that T,S,R and Q are concyclic.

T and S are not defined.
If you don't tell a little bit more about them, is going to be impossible to prove anything.
 
I suppose that T lies on PQ and S lies on PR
PS=SR
PT=TQ
This two equalities make the situation simple

At first we may notice that
If AB is a chord of a circle with centre O then the triangle OAB is an isoskeles, so the perpendicular from O to AB is at once
-perpendicular bisector of AB
-angle bisector of AOB
-altitude

The right triangles OPS,OPT are congruent (OS=OT, OP common)
So we get PS=PT
Then, it's easy to prove that the four triangles OPS,ORS,OPT,OQT are congruent
(actually there is a symmetry trough OP)


The way I use is, to prove that all perpendicular bisectors of RS,RQ,QT intersect each other at the point K.
Then KR=KS,KR=KQ,KQ=KT (so, the point K is the center of the circle we are looking for)


You can easy show that the perpendicular bisector on RQ is the line OP (using congruent triangles)

About the two other,
Take the midpoint A of RS, and respectively the midpoint B of TQ

bring the perpendicular bisector of RS, it intersects OP at the point K (theydo intersect since AK is parallel to SO and SO intersects PR)

You have the right triangle AKP,

from K bring the perpendicular line to PQ, which intersects PQ at the point B
Now, you have another right triangle BKP
But their angles BPK and APK are equal => Triangles AKP,BKP are similar
If you use that KP is common, you get that AKP and BKP triangles are congruent

So KA=KB
and you can use it to prove KR=KS=KT=KQ



I hope that helps

You can simplify further the proof if you use symmetry
Everything over OP is symmetric to everything on the other side of OP
 

Similar threads

  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 1 ·
Replies
1
Views
1K
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
7K