C.a.R. > Applications > Similarity and Angles> Trisection of Apollonius
This is not a compass and ruler construction. Move the green point, until the ray goes through the blue point. Proof that the brown angle than trisects the blue one. The two green lines are equal.
One could present this construction, such that both ends of the green line can be moved. However, we made it easier for the user by keeping one endpoint, where it belongs.