In ΔBEC, DF is a line through the mid-point D of BC and parallel to BE intersecting CE at F. Therefore, by converse of mid-point theorem F is the mid-point of CE.
Now, F is the mid-point of CE
⇒ CF=12CE
⇒CF=12(12AC) [E is mid point of AC i.e. EC = 12AC]
⇒CF=14AC
Hence proved