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20. A lifeguard can run on sand at speed v1 and swim at speed v2 and will take path AOB as shown below to minimize the time to rescue a swimmer at point B. Let COD = L, find the distance x where the water is entered and use that value to prove that -1 1 _ sin 01 U2 sin 02 This result is called Snell's Law of optics and is an example of a very deep principle in physics known as Fermat's principle of least time. Much of your future theoretical upper division and graduate work will involve applications of this idea. A Sand speed = vi L1 C X 61 0 L-x D 82 Ocean speed = v2 LZ B