As shown in the figure, it is known that in △ ABC, ab = AC, D is a point on the CB extension line, ∠ ADB = 60 °, e is a point on ad, and de = dB

As shown in the figure, it is known that in △ ABC, ab = AC, D is a point on the CB extension line, ∠ ADB = 60 °, e is a point on ad, and de = dB

It is proved that in △ abd and △ ACF, ab = AC, ab = AC, ABC = ACB, abd = ACF, ab = AC, abd = acfbd = CF, abd = SAS, ad = AF, and ADB = 60 °, ADF is an equilateral triangle, ad = DF, ad = AF