Geometry Stumper

[Albert Chan]

(08-15-2018 09:46 PM)Thomas Puettmann Wrote:  Once you know that the line DC is the angular bisector of the exterior angles at C, you are done
(by symmetry, the line EC is the same angular bisector).

That reminds me of a book I read, "The Man Who Love Only Numbers".

Erdos once said, "You don't have to believe in God, but you should believe in the Book"

Your proof should belong in the Book.

Volemar already proved the green right angle, and is so close to the proof.
Just say, "by symmetry, the other side also got a right angle", and the proof is done.

Too bad ...