Geometric/algebraic proof of a quadratic

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    Proof Quadratic
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Discussion Overview

The discussion revolves around constructing a geometric and algebraic proof related to a quadratic equation, specifically focusing on the existence of points M and N in relation to a circle and line segments defined by points P' and Q'. The scope includes both geometric reasoning and algebraic manipulation.

Discussion Character

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

Main Points Raised

  • One participant expresses uncertainty about how to construct an algebraic proof from a given geometric representation and questions if they missed something obvious.
  • Another participant suggests that the question may be poorly framed, noting that varying the value of c could prevent the line P'Q' from intersecting the circle, thus questioning the existence of points M and N.
  • Some participants propose that if points M and N exist, then segments QX and QY could represent the roots of the quadratic equation.
  • There is a suggestion to find the coordinates of points M and N, assuming they exist, as a potential method of solving the problem.
  • One participant notes that varying points P' and Q' could lead to intersections with the circle at points M and N, indicating a consistent construction.
  • A later reply mentions that if one is familiar with coordinate geometry, they could translate the proof into a different form, possibly using the gradient of line P'Q' without relying on coordinates.

Areas of Agreement / Disagreement

Participants express differing views on the clarity of the problem statement and the conditions under which points M and N can be found. There is no consensus on how to approach the proof or the existence of the points in question.

Contextual Notes

There are limitations regarding the assumptions about the existence of points M and N, as well as the dependence on the definitions of the geometric elements involved. The discussion does not resolve the mathematical steps necessary for the proof.

raphael3d
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http://img717.imageshack.us/img717/4029/screenshot20110106at123.png

i don't know how to construct an algebraic proof from this or how to attempt it.
is there anything obvious which i missed?


thank you
 
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I think the question is badly put. By varying the value of c, one can ensure that P'Q' does not cut the circle. So there would be no M and N.

Perhaps they mean that if there is an M and N, then QX and QY will be the roots of the equation.

One way you could solve it is:
- find the coordinates of N and M, assuming they exist
... rest removed.
 
Last edited:
one can then also vary P' and Q' so they do cut the circle at points M and N, so the construction seems consistent.

its an example from "course in pure mathematics" from g.h.hardy

how should one find points like M and N, if only lengths are given and asked?
this is no function space, just geometry.

for instance: QN/2=NY/QY, but how could someone proceed then?
 
If you know how to solve it with coordinate geometry, you can translate the proof to the form you require. For example, using the gradient of P'Q' is possible without coordinates.
 

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