Question 71
Let $H$ be the orthocentre of an acute triangle $ABC$. The line through $A$ perpendicular to $AC$ and the line through $B$ perpendicular to $BC$ intersect at $D$. The circle centred at $C$ through $H$ intersects the circumcircle of $ABC$ at $E,F$. Prove $|DE|=|DF|=|AB|$.
