Geometry Stumper

[Thomas Puettmann]

(08-15-2018 12:39 AM)Albert Chan Wrote:  I "see" the solution !

Great! "Seeing" is the great fun in geometry, and it is almost entirely training.

Attached is what I have sketched after I read your original post.

The original triangle is in grey, the bisectors given in the problem are in red and blue and what you get for free is in green. That is, line DC is the bisector of the exterior angles at C (which is perpendicular to the bisector of the interior angle because the exterior and interior angle sum up to 180°).