Re: sin x / x tends to 1...

Lee Rudolph wrote:

> From this it follows that, *if you believe* that sin
> has a (non-zero) derivative *at all*, at any point,
> then its derivative is cos. Can that belief be justified
> without assuming the limit under consideration?
> I suspect it can, by further geometric argument using the
> helix parametrized by x \mapsto (cos(x), sin(x), x).

How would the argument go?


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