I want to compute following:
$$ \lim_{x \rightarrow 0} \frac{x-\sin(x)}{x-\tan(x)}$$
I have tried to calculate this with l’Hôpital's rule. l’Hôpital's rule states that:
$$ \lim_{x\rightarrow a} \frac{f(x)}{g(x)}=\lim_{x \rightarrow a } \frac{f'(x)}{g'(x)} $$
Now i can get to the right result with l’Hôpital's rule but it took a little over two pages on paper. Had to use l’Hôpital's rule 4 times. How do you solve this without l’Hôpital's rule ?
The result appears to be(with l’Hôpital's rule):
$$ \lim_{x \rightarrow 0} \frac{x-\sin(x)}{x-\tan(x)}=-\frac{1}{2} $$
If someone can provide alternative solution to this problem that would be highly appreciated.
Answer
Utilizing the Taylor expansions
$\sin(x)=x-\frac{1}{6}x^3+\mathcal{O}(x^5)$
$\tan(x)=x+\frac{1}{3}x^3+\mathcal{O}(x^5)$, we get
$\frac{x-\sin(x)}{x-\tan(x)}=\frac{x-(x-\frac{1}{6}x^3+\mathcal{O}(x^5))}{x-(x+\frac{1}{3}x^3+\mathcal{O}(x^5))}=\frac{\frac{1}{6}x^3+\mathcal{O}(x^5)}{-\frac{1}{3}x^3+\mathcal{O}(x^5)}\to-\frac{1}{2}$ as $x\to0$.
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