Limits of Taylor Series: Is $\sin x=x+O(x^2)$ Correct?

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SUMMARY

The discussion centers on the mathematical expression of the Taylor series for the sine function, specifically the notation $\sin x = x + O(x^2)$ versus $\sin x = x + O(x^3)$. It is established that while both notations are technically correct, using $O(x^3)$ provides more precise information by indicating the absence of an $x^2$ term. The limit $\lim_{x \to 0}\frac{\sin x - x}{x^3}$ must be bounded for the expression to hold true.

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LagrangeEuler
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We sometimes write that
\sin x=x+O(x^3)
that is correct if
\lim_{x \to 0}\frac{\sin x-x}{x^3}
is bounded. However is it fine that to write
\sin x=x+O(x^2)?
 
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Yes, but you give away information. You could even say ##\sin x = O(x).##
 
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Writing ##O(x^3)## says there is no ##x^2## term.
 
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