Divide ABCDE into two parts with equal area

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Discussion Overview

The discussion revolves around the problem of dividing a pentagon ABCDE into two parts with equal area by constructing a line through point A. Participants explore various approaches and conditions related to this geometric problem.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asks whether ABCDE is a general or particular pentagon.
  • Another participant suggests that for a regular pentagon, constructing the midpoint of segment CD and drawing a line from A to that midpoint will divide the area equally.
  • A participant refers to a solution involving a midpoint M of segment PQ, stating that the line AM will divide the pentagon into equal areas if M lies between points C and D, although they express uncertainty about proving this condition.
  • Another participant mentions the concept of a "proof without words" and emphasizes the importance of a diagram to illustrate the solution.
  • Concerns are raised about the condition that M lies between C and D, with one participant arguing that this is not always true and suggesting that M could coincide with C or D, or even lie between other points depending on the lengths of the segments.

Areas of Agreement / Disagreement

Participants express differing views on the conditions under which the proposed methods will work, indicating that there is no consensus on the necessary conditions for dividing the pentagon into equal areas.

Contextual Notes

Participants note that the assumptions regarding the positions of points and the lengths of segments may affect the validity of the proposed solutions, highlighting the need for further exploration and clarification.

Albert1
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ABCDE is a pentagon,please construct a line (passing

through point A),and divide ABCDE into two parts with equal

area
 
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Is this a general pentagon, or a particular pentagon?
 
For a regular pentagon, just construct the midpoint of $CD$, call if $F$, and draw the segment $AF$. This splits the pentagon in two equal pieces.
 
Prove It said:
Is this a general pentagon, or a particular pentagon?
A general pentagon(convex)
 
Albert said:
ABCDE is a pentagon,please construct a line (passing

through point A),and divide ABCDE into two parts with equal

area
http://www.mathhelpboards.com/attachments/f28/998d1373594278-change-pentagon-into-triangle-equal-area-pentagon.jpg

Referring to Albert's beautiful solution to the problem in http://www.mathhelpboards.com/f28/change-pentagon-into-triangle-equal-area-5486/, if $M$ is the midpoint of $PQ$ then the line $AM$ will do the job, provided that $M$ lies between $C$ and $D$. I imagine that this must necessarily be the case, but I don't see how to prove it.
 
In my opinion the best proof is "a proof without words"
so again I construct a diagram and let it explain the solution
View attachment 1033
and AG is what we need as written by Opalg
"if [FONT=MathJax_Math]M is the midpoint of [FONT=MathJax_Math]P[FONT=MathJax_Math]Q then the line [FONT=MathJax_Math]A[FONT=MathJax_Math]M will do the job"
 

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    pentagon02.jpg
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Last edited:
Opalg said:
Referring to Albert's beautiful solution to the problem in http://www.mathhelpboards.com/f28/change-pentagon-into-triangle-equal-area-5486/, if $M$ is the midpoint of $PQ$ then the line $AM$ will do the job, provided that $M$ lies between $C$ and $D$. I imagine that this must necessarily be the case, but I don't see how to prove it.
The statement M lies between C and D is not always true
in fact M and C (or M and D)may coincide
May M also lie between D and E ?(if the length of CD is very small)
M may also lie between B and C.
(we may check this using various diagram)
 
Last edited:

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