perplexus.info :: Geometry : Obtuse triangle from equilateral triangle

Obtuse triangle from equilateral triangle (Posted on 2023-08-14)

Let ABC be an equilateral triangle with point D on AC.

Create a new triangle with side lengths AD, DC, BD.

Prove one angle of this new triangle is 120 degrees.

No Solution Yet Submitted by Jer

Rating: 4.5000 (2 votes)

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re: Another solution

| Comment 3 of 4 |

(In reply to Another solution by Brian Smith)

Very nice, Brian. I always like a geometric proof, and this one rates an "aha!".

Posted by Steve Herman on 2023-08-15 00:56:10

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