Analyze by Maclaurin formula:
Do you know the 'formula' for ex? If so, try substituting ix for x.
You could also do it by looking at the power series of cosx and sinx, and then multiply the sine power series by i and then add the power series of cos on to it, so you get [itex] cosx + isinx [/itex]. Either way will get you the same answer, and the first method would probably be a little quicker.
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