Monday 29 December 2014

real analysis - Find $lim_{x to 0} frac{ln (x^2+1)} {x^2} $ without L'hopital's rule



I have to find the limit without L'hopital's rule:
$$\lim_{x \to 0} \frac{\ln (x^2+1)} {x^2} $$




Is it possible?
I thought about using squeeze theorem or something, but it didn't work out.



Hints are more than welcome!



P.S - I didn't study Taylor series or Integrals yet.


Answer



$$\begin{align}
\lim_{x \to 0} \frac{\ln (x^2+1)} {x^2}&=\lim_{x \to 0} \ln (x^2+1)^{\frac{1}{x^2}}\\

&=\ln\left(\lim_{x \to 0} (x^2+1)^{\frac{1}{x^2}}\right)\\
&=\ln e=1
\end{align}$$


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