Monday, May 1, 2017

Question about limit limlimitsnrightarrowinftycosnleft(fracomegasqrtnright)

My question is how to calculate this limit. lim I know that the answer is e^{-\frac{\omega^2}{2}}.


Attempts: I tried to reduce the limit to the known limit \lim_{n\rightarrow \infty}\left(1+\frac{a}{n}\right)^n=e^{a} So, I wrote \cos\left(\frac{\omega}{\sqrt{n}}\right)\approx1-\frac{\omega^2}{2n} using the cosine Taylor series, and stop there because \frac{\omega}{\sqrt{n}} gets very small as n\rightarrow \infty. Then, the limit is \lim_{n\rightarrow\infty}\cos^n\left(\frac{\omega}{\sqrt{n}}\right)=\lim_{n\rightarrow \infty}\left(1-\frac{\omega^2}{2n}\right)^n=e^{-\frac{\omega^2}{2}}


I also tried using \cos(x)=\frac{e^{ix}+e^{-ix}}{2} and then using the binomial theorem with no success.


Is this answer correct?

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