Question 28
Let $\triangle AB\Gamma$ be an acute angled triangle with circumcircle $c(O, R)$. From the midpoint $\Delta$ of the side $B\Gamma$ we draw a line $\varepsilon$ perpendicular to $AB$ which meets $AB$ at $E$. If the line $AO$ intersects the line $\varepsilon$ at $Z$, prove that the points $A$, $Z$, $\Delta$, $\Gamma$ are cyclic.