Let a Triangle $\triangle ABC$ be inscribed in a circle, along the arc $\overset{\frown}{BC}$ lies a point $P$ such as, $BP=4\sqrt{2}$.

Compute the distance between the two orthocenters of the triangles $\triangle ABC$ and $\triangle APC $.
- As you can see form the picture above the segment $BP$ seems to be parallel with "AC""$H_1H_2$". But I don't know how to prove it. I believe something about the nine point circle might be useful.