Sunday, March 4, 2018

trigonometry - How is $frac{sin(x)}{x} = 1$ at $x = 0$





I have a function:
$$\text{sinc}(x) = \frac{\sin(x)}{x}$$
and the example says that: $\text{sinc}(0) = 1$, How is it true?



I know that $\lim\limits_{x \to 0} \frac{\sin(x)}{x} = 1$, But the graph of the function $\text{sinc}(x)$ shows that it's continuous at $x = 0$ and that doesn't make sense.


Answer




In an elementary book, they should define $\mathrm{sinc}$ like this
$$
\mathrm{sinc}\; x = \begin{cases}
\frac{\sin x}{x}\qquad x \ne 0
\\
1\qquad x=0
\end{cases}
$$
and then immediately prove that it is continuous at $0$.




In a slightly more advanced book, they will just say
$$
\mathrm{sinc}\;x = \frac{\sin x}{x}
$$
and the reader will understand that removable singularities should be removed.


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