I found this question here :
Evaluate cos(z), given that z=ilog(2+√3)
It says that -
e−iz=cos(z)−isin(z)
isn't necessarily true because sinz is imaginary (for the particular value of z in the link). But, the proof of Euler's formula using Maclaurin series suggests that it should be valid for complex arguments too. What am I missing?
Answer
No, it doesn't say that eiz=cos(iz)−isin(iz)is not necessarily true! It is true. What it says in that other answer is that cos(iz) is not necessarily the real part of eiz.
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