An Isosceles Triangle Theorem

In the figure, ABD is an isosceles triangle with AB = BD.

Also AE = CD.

F is the intersection of AD and EC.

The theorem states that EF = FC.

We also see the ratio of AF / FD. Can you come up with a formula for this ratio in terms of AB, AD and AE?

Learn more about this Isosceles Triangle Theorem in our Geometry Formula Atlas

If you are interested in this applet, you may like our Interactive Symbolic Geometry software Geometry Expressions.