Question 37
Let $ABC$ be an acute angled triangle inscribed in a circle $c(O, R)$ and $F$ a point on the side $AB$ such that $AF \lt \frac{AB}{2}$. The circle $c_1(F, FA)$ intersects the line $OA$ at point $A'$ and the circle $(c)$ at $K$. Prove that the quadrilateral $BKFA'$ is inscribed in a circle passing through $O$.