Problem:
Let be a triangle where , with circumcenter and incenter . The angle bisector of intersects the circumcircle of in and . Let be the projection of onto , and be the projection of onto . Prove that bisects .
Problem:
Let be a triangle where , with circumcenter and incenter . The angle bisector of intersects the circumcircle of in and . Let be the projection of onto , and be the projection of onto . Prove that bisects .
Solution:
Because is the midpoint of , it suffices to show that is parallel to , as the result follows by simply looking at a homothety centered at .
So first of all by looking at the problem we instantly recognise the point as the circumcenter of , as this is a well known configuration. So from this we and . Next up we find to be parallel to , as they both are perpendicular to . From this we get . We now have two same angles at and and also . This gives us motivation to look at perpendicular bisector of , as it goes through and . If we can show that is also isosceles, then it'll instantly follow that , which then will give us parallel to as wanted. So now for the fun stuff; more angle chasing.
We easily calculate . From this we get that and thereby that the angle bisector of and coincide. And as the angle bisector of is equal to the perpendicular bisector of , we have . Finally using the cyclic quadrilateral we have , which finishes the proof as explained before.

Let be the intersection of and