In the figure, point D lies on the side of AC in \triangle ABC, AC=25 , AB=35. Point E and F are movable on the side of AB (point F is on the left of point E) and \angle EDF=\angle A

If DF\perp AB , find the length of AE

Let x=AE , y=AF, determine the function y in terms of x and the domain of the function;

Connect CE, if \triangle DEC and \triangle ADF are similar, find the value of x