How Does Light Reflect in an Ellipse to Connect Its Foci?

[Sobhan]

I needed the proof of this:if a ray of light passes from one focus of an elipse after reflection it will pass the other focus.please i need the one only using the fact that i=r ( not the fermat rule)

 

[RUber]

In reference to the attached image, what do you know about length of segment d2 compared to the distance 2*c between the foci?