With apologies to Professor Rubin

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Last week I wrote a couple of blogs, as a way of explaining to myself, about the way in which a Taylor expansion could approximate for a function and in doing so, quoted L’Hospital’s rule.

Professor Paul A. Rubin, of Michigan State University (to whom I now owe a whole night of drinks), pulled me up about my use of L’Hospital’s rule.

I have to confess I did not quite follow his point – but having watched the video below, I now do: L’Hospital’s rule solves \frac{f(x)}{g(x)} for a particular point, not for the whole domain of x .