Isosceles Triangle has Two Equal Angles/Also known as
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Isosceles Triangle has Two Equal Angles: Also known as
This proposition is the famous pons asinorum, that is, the bridge of donkeys, supposedly for two reasons:
- $(1): \quad$ The diagram accompanying it is supposed to look a bit like a bridge
- $(2): \quad$ If you can't cross this bridge (that is, understand this theorem), you're supposedly a bit of a donkey.
Don't blame the students -- this is one of the more tortuous ways of proving this theorem.
Commentators have speculated that Euclid may not have known what he was doing when he wrote this.
Sources
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): pons asinorum
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): pons asinorum
- 2008: Ian Stewart: Taming the Infinite ... (previous) ... (next): Chapter $2$: The Logic of Shape: Euclid
- 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): pons asinorum
- 2021: Richard Earl and James Nicholson: The Concise Oxford Dictionary of Mathematics (6th ed.) ... (previous) ... (next): pons asinorum