When we talk about differentiability on a(adsbygoogle = window.adsbygoogle || []).push({});

Set X, the set has to be open.

And if a set X is open there exists epsilon> 0 where epsilon is in R.

Then if x is in X, y=x+ or - epsilon and y is also in X

But this contradicts to what i was taught in highschool; end points are excluded in the open interval.

Could anyone clarify this for me?

Also, since epsilon is arbitrary number, if set it to be infinite then would X be R?

(Entire Real number set)

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# I Open interval (set) end points and differentiability.

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