Let $H$ be the orthocenter of an acute triangle $ABC$. Prove that the triangle formed by the circumcenters of triangles $ABH$, $BCH$ and $CAH$ is congruent to $ABC$.
I have already seen many answers on MSe But my doubt is diffferent,
In this solution (first one ) https://artofproblemsolving.com/community/c618937h1628954_problem_320_bamo_20133
To prove $O_AB || O_BA$, we can do some angle calculations: $\angle O_ABC = 90 - A$, and $\angle C A O_B = 90 - B$
how he got $\angle O_ABC = 90 - A$, and $\angle C A O_B = 90 - B$ ? I tried some angle chasing but did not able to get this ..thankyou