In the figure, is a \triangle ABC in which, \angle ACB =90\degree , AC=3 , BC = 4 , and point D , E are two points on the side of AB ( not coincide with D , E ) , and \angle DCE = \angle B .

If CD\perp AB ,find the value of the length of BE

If \triangle CDE is an isosceles triangle, find the length of AD

If AD=x , BE=y , find function y in terms of x and the domain of the function.