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Why is it that the graphs of tan inverse and sin in the interval $$\left[-\frac \pi 2 , \frac \pi 2\right]$$ are so similar.

Is it just some coincidence or something deeper?

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  • $\begingroup$ What are your thoughts on this problem? They are both functions used in trigonometry: of course they are similar. $\endgroup$ – clathratus Mar 20 at 20:01
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It's nothing deep.

Both $f(x) = \arctan x$ and $g(x) = \sin x$ are increasing on $(-\pi/2,\pi/2)$ and both have an inflection point at $x = 0$. Their somewhat similar appearance is due to those properties and the fact that $\arctan \dfrac \pi 2$ is remarkably close to $1$.

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The first few terms of their Taylor series around $0$ are $x-x^3/6+x^5/120$ and $x-x^3/3+x^5/5$, respectively, so it’s not terribly surprising that they look similar in a relatively small interval around the origin. I doubt that there’s any deep connection beyond that, though.

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