How does Fermat's Principle apply to the concept of Heroes?

[nokia8650]

http://img26.imageshack.us/img26/2615/43774076.th.jpg

Can someone please explain how to do this problem - I don't really know where to start.

Thanks

 

[cepheid]

Hi nokia8650,

The nice thing about Hero (of Alexandria)'s proof is that it is quite simple. A' is the image of A. Therefore, by symmetry, AC = A'C. Therefore, determining the shortest possible distance traveled between A and B reduces to a problem of determining the shortest possible distance between A' and B. But what is the shortest possible distance between two points? ;)

 

[nokia8650]

Ah yes, i makes sense now. Thank you so much.