Compass and Straightedge proof that two lines are segments of one straight line

bphil

New member
Joined
Apr 25, 2013
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5
Dear forum,

I found a reference to a proof in an ancient text that is supposed to show that two lines are actually two segments of one straight line.
What the author appears to have in mind is the following:

1) You have a rectangle ABCD
2) You draw the diagonal BC and bisect it at point E
3) You draw the lines AE and DE

Now the author says that he needs to prove that AE and DE form a straight line AD.

I wonder how a proof entirely based on straightedge and compass would look like. Any hints?

Thanks!
 
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