As shown in the figure: in known quadrilateral ABCD, ab = ad, AE, AF divide ∠ BAC and ∠ CAD equally

As shown in the figure: in known quadrilateral ABCD, ab = ad, AE, AF divide ∠ BAC and ∠ CAD equally

Because AE and AF divide ∠ BAC and ∠ CAD equally
So AB / AC = be / EC, AD / AC = DF / FC
And because AB = ad
So be / EC = DF / FC
CE/BC=CF/DC
EF∥BD