Wednesday, September 12, 2018

trigonometry - How is fracsin(x)x=1 at x=0


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


I know that lim, 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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