Triangle ABF is isosceles with apex A. This implies AB=AF. D is the midpoint of BF, which implies BD=DF. E is the midpoint of CE, so this statement appears to have a typo and should probably state that E is the midpoint of CF, so CE = EF. We are asked to prove that triangle ACE is isosceles.
Since ABF is an isosceles triangle with apex A, we have AB ≅ AF. Since D is the midpoint of BF, we have BD ≅ DF. We assume that the problem meant to say E is the midpoint of CF, which gives CE ≅ EF.
In triangles ABD and ADF, we have AB ≅ AF, BD ≅ DF and AD ≅ AD (common side). So, by SSS congruence, triangles ABD and ADF are congruent. Therefore, corresponding angles are congruent: ∠BAD ≅ ∠FAD, ∠ADB ≅ ∠ADF, and ∠ABD ≅ ∠AFD.
We want to show that triangle ACE is isosceles. We need to show either AC=AE or AC=CE or AE=CE. Using the given information, there's no apparent way to achieve this. Assuming E is the midpoint of CF was crucial in demonstrating the congruence of triangles ABD and ADF, but it doesn't directly help to prove triangle ACE is isosceles. It appears there may be missing information or a possible error in the original problem.