Ever wonder how a mirror works? If you want to find the path that light takes when reflecting off a surface, you could use Fermat's Principle. This states something like this: The path that light takes is the path that takes the least time. When going from point A to point B, light will travel along the path that takes less time than any other options. I actually used this idea in a question for my students learning about the variational principle with a question using Fermat's Principle.

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