DA = DB？ ∴? DE/DF=BE/BD？ And then what? Angle EDF = 60 = angle B.

So triangle DEF∽ triangle BDE∽ triangle ADF

2)EF/FD=FD/AF？ AF=4-X？ FD^2=Y(4-X)

In triangle AFD? FD 2 = x 2-6x+ 12 (long solution triangle using AF and AD)

∴Y=(X^2-6X+ 12)？ /? (4-X)？ Domain name? 4 & gtx & gt3? (EC does not overlap because of the extension line of BC? X is not equal to 3; Point f does not coincide with point a, so it cannot be equal to 4)