(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

I did the question with help, but did not understand why did we multiply e^-i(x/2)

How do I know what to multiply for getting the real part of a complex number in exponential form?

2. Relevant equations

3. The attempt at a solution

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# Homework Help: Deriving Lagrange's Trig Identity (real part of a complex number in exponential form)

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