Hello. Please tell me how do I derive:(adsbygoogle = window.adsbygoogle || []).push({});

cos(θ)=1/2 ([itex]e^{iθ}[/itex]+[itex]e^{-iθ}[/itex])

from:

[itex]e^{iθ}[/itex]=cos(θ) + isin(θ)

as well as:

sin(θ)=1/2i ([itex]e^{iθ}[/itex]-[itex]e^{-iθ}[/itex])

I can't figure it out...for example, where does the 1/2 come from? Thank you

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# Euler's identity question

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