Proof that all triangles are isosceles

[Konstantinos88]

That is my Greek-Euclidean proof that all triangles are isosceles. Any doubts?

 

[RPinPA]

Is this different from Lewis Carroll's proof of the same "theorem"?

He had a couple of these fallacious proofs, which are a lot of fun to try to analyze. The error is subtle. I won't spoil the fun yet.

Is your last line in Greek the same meaning as the traditional Latin closing "quod erat demonstrandum" (QED)?

 

[Konstantinos88]

Is your last line in Greek the same meaning as the traditional Latin closing "quod erat demonstrandum" (QED)?

Yes, exactly this: The phrase, quod erat demonstrandum, is a translation into Latin from the Greek ὅπερ ἔδει δεῖξαι (hoper edei deixai; abbreviated as ΟΕΔ).
https://en.wikipedia.org/wiki/Q.E.D.

 

[mfb]

A nice way to draw the sketch to hide the flaw.