Thursday, 9 May 2019

calculus - Finding limntoinftyfrac12n1cot(fracx2n)





Find: lim




Can L' Hopital's rule be used to solve this? And differentiate it with respect to x or n?



What I've found is that



\begin{equation} \lim_{n \to \infty} \frac{1}{2^{n-1}}\cot\left(\frac{x}{2^n}\right) = \lim_{n \to \infty} \frac{\frac{1}{2^{n-1}}\cos\left(\frac{x}{2^n}\right)}{\sin\left(\frac{x}{2^n}\right)} \end{equation}




which is of the form \frac{0}{0}, but I don't know how to go further from here. Any help is appreciated.


Answer



Hint:
\lim_{x\to 0}\frac{\sin x}{x}=1
and
\lim_{x\to 0}\cos x =1.


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