Problem

Source: 2013 All-Ukrainain Correspondence MO of magazine ''In the World of Mathematics'', grades 5-12 p7

Tags: geometry, collinear, right triangle, Ukraine Correspondence



An arbitrary point $D$ is marked on the hypotenuse $AB$ of a right triangle $ABC$. The circle circumscribed around the triangle $ACD$ intersects the line $BC$ at the point $E$ for the second time, and the circle circumscribed around the triangle $BCD$ intersects the line $AC$ for the second time at the point $F$. Prove that the line $EF$ passes through the point $D$.