Find all values for cos(i) In my Differential Equations class recently we have learned about Euler's Formula and Fourier Series. I am given the problem Find all values for cos(i) where i = sqrt(-1). There is a long list of similar problems, but I figure if I can get some help on one of them I can learn to do the rest. If possible, could an answer show me not all the work, but maybe just show me where to start? I want to learn how to get the answers myself, not just be given answers.

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