Triangle and two circles theorem

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Discussion Overview

The discussion revolves around the theorem involving a triangle and two circles, specifically focusing on the relationship between the inscribed circle (incircle) of a triangle and a circle that passes through the midpoints of the triangle's sides. Participants are exploring the proof and implications of this theorem, seeking clarification and accessible explanations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses difficulty in forming a Cartesian equation for the two circles involved and requests an accessible explanation of the theorem.
  • Another participant identifies the topic as related to the incircle of a triangle and provides a geometric argument involving tangents and congruent triangles to explain the relationship between the incircle and the triangle's sides.
  • A third participant references an external resource that may provide additional diagrams and explanations relevant to the discussion.

Areas of Agreement / Disagreement

There is no clear consensus on the understanding of the theorem, as participants are at different levels of familiarity with the concepts involved. Multiple viewpoints and approaches are presented without resolution.

Contextual Notes

The discussion includes various assumptions about geometric properties and relationships that are not fully resolved, such as the specifics of the Cartesian equations and the implications of the tangent properties discussed.

Delong
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Can someone help me understand why this is the case? I tried forming a cartesian equation for the two circles but there were too many variables that it would be too messy to compute. Otherwise I am rather stuck on how to do it. I would appreciate it if someone can explain how to prove this theorem in accessible terms. Thanks.

In a triangle the inscribed circle touches the circle that passes through the midpoints of the sides.
 

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I have no idea what the 'two circles theorem' is but you seem to be discussing the incircle for a triangle.

The inscribed circle for any polygon is the circle to which each side is tangent.

To see why the tangent point is the mid point of each side look at my first sketch for some preliminary results.

From any point P outside any circle, centre O, two tangents may be drawn meeting the circle at M and N.
Since OM and ON are radii and NP and MP are tangents \hat{ONP} and \hat{OMP} are right angles.
Since OP is common to both triangles OMP and ONP they are congruent.

Therefore \hat{NPO} = \hat{MPO}
Therefore OP bisects \hat{NPM} and the two tangents
Therefore OP bisects any line such as MN, crossing PM and PN produced

Taking this result into my second diagram you can see that the line from each vertex of triangle ABC to the centre of the incircle produced bisects the vertex angle and the opposite side.
Further these lines meet the opposite sides at right angles, since OF, OG, OH are radii and the sides are tangents.
Further these lines meet at the centre of the incircle.

go well
 

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So yes I will read these very soon. Thanks!
 

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