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Search Loci: Convergence:
I have had my results for a long time: but I do not yet know how I am to arrive at them.
In A. Arber The Mind and the Eye 1954.
Among people with some mathematical background, Euler may well be best known for Euler’s formula: eix = cos x + i sin x (also often referred to as the Euler-Cotes formula). In examining the relation between exponentials and trigonometry, Roger Cotes (1682-1716) came to the formula ix = log(cos x + i sin x). This appeared in his Logometria of 1714 (printed in the Philosophical Transactions of the Royal Society, then a widely read publication) and reprinted in his posthumous 1722 work Harmonia Mensurarum. In this work Cotes studied logarithms and their relation to hyperbolas. Defining the “modulus and modular ratio” as the ratio of the number 1 to the factorials, he found the same terms as Euler did in his series expansion above. In particular, Cotes stated the ratio of 2.718281828459 to 1. Thus even our attribution of the decimal expansion of e to Euler is erroneous. But as we saw above, Euler did originally use c. If he had continued with that, urban legend might now say that he named it after Cotes, which would be correct in that Cotes was the first to explicitly write out the numerical approximation for the series expansion.
Shell-Gellasch, Amy, "Napier's e," Loci (December 2008), DOI: 10.4169/loci003209
rational approximation of an irrational number
students find it really curious, and more intriguing when i tell them that (1+(1/n))^n in the limit of n tending to infinity is an irrational number 'e'. Here n is a positive integer. They find it really difficult to believe that a rational expression on the left hand side tends to an irrational number. How do I convince them ?
Geometrical introduction of Napier's e
Usually Ludolph's number is introduced geometrically as the "perimeter to diameter number" of any curve of constant distance to a center-point. So why shouldn't we introduce Napier's number in a more or less similar way as the "tangent-point-height to base-point-height number" of any curve of constant relative growth ? Here we refer to the following property: Chose an arbitrary point T on an arbitrary growth curve (exponential curve) g with base line (asymptote) b. Let B be the point of intersection of b and the tangent line at T. Let B' be the point of intersection of g and the perpendicular to b containing B; and let T' be the point of intersection of b and the perpendicular to b containing T. It can be proved that line segment T'T measured with BB' gives Napier's number. I would like to learn about publications in which this geometrical approach is mentioned.