Geometry Stumper

[Albert Chan]

(08-15-2018 11:56 AM)Voldemar Wrote:  Aha. But do not forget to prove why circle with center D touch line AC.
Because AD is the bisector of angle CAF.
Your solution is nice.

Good catch.

Technically, you have to proof that circle really inscribe the lines from the outside.
(like you did with why circle touch AC, but need 2 more to complete proof)

Cecil's prove only uses triangles. (see my first post for link)

He likely know about the circle, but it required more explanations to readers in his column.
Instead, he proved backwards (not using circle), showing DF = DG = DH

BTW, have you peek at Thomas Puettmann sketch, about the green lines ?
Why is that a right triangle ?