Talk:Exponentiation/Archive 2023

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What do the dots mean please?

I am a modestly intelligent UK beginner wishing to understand from Wikipedia about Exponentiation, as a stepping-stone to understanding what logarithms are and why one wants them. Simple, eh? To me, the lede paragraph of this article is clearly well-constructed, but becomes meaningless when the special dots start to be introduced into the mathematical examples. For instance, in the first example $$b^{n}=\underbrace {b\times b\times \dots \times b\times b} _{n{\text{ times}}}.$$ I understand that the three dots represent a kind of space-filler, expressing the variable number of possible multiplications of the base represented by the integer n. Are they, therefore, within the normal range of algebraic notation, or are they an extraneous usage (meaning something like "extended to the corresponding number"), rather like the dots used to transcribe unreadable letters in manuscript texts - ? Taking the latter to be the case, I make sense of the next examples on the same principle, but then I come to a puzzling set of equations where the single dot is employed:

"In other words, when multiplying a base raised to one exponent by the same base raised to another exponent, the exponents add. From this basic rule that exponents add, we can derive that $b^{0}$ must be equal to 1, as follows. For any $n$, $b^{0}\cdot b^{n}=b^{0+n}=b^{n}$. Dividing both sides by $b^{n}$ gives $b^{0}=b^{n}/b^{n}=1$."

Here, in the formulation $b^{0}\cdot b^{n}=b^{0+n}=b^{n}$ the single dot does not stand for a missing number, but apparently represents a mathematical operation or relationship (?addition or multiplication, or merely juxtaposition or sequence?) which has not been explained to the reader.

The problem gets worse when one comes to the formulation in the next lines, $(b^{1})^{3}=b^{1}\cdot b^{1}\cdot b^{1}=b^{1+1+1}=b^{3}$, where the dot clearly cannot mean the same as it did in the first example. Here the two dots seem to separate the products of three similar mathematical operations while holding those products distinct from one another within a group.

The question arises, to an uninformed reader, What does the dot mean? Being unenlightened, I would be most sincerely grateful for the explanation. Eebahgum (talk) 23:34, 8 January 2023 (UTC)

The meaning of the three dots (ellipsis) is almost the same as in common language; for details, see ... § In mathematical notation.

The centered dot is a standard notation for multiplication. It is an anomaly that three different notations are used for multiplication in this article. I have added an explanatory footnote for clarification, but the article must be further edited (see the next section). D.Lazard (talk) 10:17, 9 January 2023 (UTC)

Thankyou for your response, which I found very helpful. I have added a comment to the thread below. Eebahgum (talk) 18:16, 9 January 2023 (UTC)

Why did this article fall from grace?

In the past, this article was considered as "good" right?

Later, that status has been revoked. How did such happen?

Learning why it happened should be a good idea to help make this article better. - S L A Y T H E - (talk) 17:11, 4 March 2023 (UTC)

Definition of principal value of log(z)

In the section:

Principal value

[...]

and the imaginary part of z satisfies

-π < Im (z) < π [this does not make sense to me: Isn't it a condition on the Arg(z) or equivalently on the Im(log(z))? Since log(z)=log(|z|)+i(Arg(z)+2nπ), n in Z and the principal value of log(z) can be defined as Log(z) when chosing -π < Im(log((z))=Arg((z)) < π, i.e. n=0]

[...] 217.10.52.10 (talk) 09:52, 20 April 2023 (UTC)

 Fixed. D.Lazard (talk) 16:12, 21 April 2023 (UTC)

Three notations for multiplication

This article uses 3 different notations for multiplication. IMO, either $\times$ must be replaced with $\cdot ,$ or $\cdot$ must be replaced by $\times ;$ in any case, some occurrences of $\cdot$ should be removed, especially in exponents. As I have no clear opinion on the best choice, I wait for a consensus here. For clarification (see the preceding thread), I have added an explanatory footnote. D.Lazard (talk) 10:28, 9 January 2023 (UTC)

As you wrote in the first thread, the primary issue with using $\cdot$ is that it becomes ambiguous whether this represents ellipses or multiplication (to be fair, it's not really ambiguous, because one could figure out from context that one dot means multiplication and three means ellipses). So, I think that defaulting to $\times$ in this article is probably best, even though this notation feels quite elementary-school-y. Duckmather (talk) 15:20, 9 January 2023 (UTC)

Now that I know what is meant, I would suspect that most uninitiated readers (in the UK at least) would recognize a $\times$ sign as a multiplication sign, but that the $\cdot$ sign for multiplication would be much less familiar, and might well be a source of confusion. Additionally, I have come to this article in following-up work on the biographical WP article on William Oughtred, and I find that the introduction of the $\times$ sign, in W.O.'s Clavis Arithmeticae (1631), followed on very soon after, and in the context of, the description of logarithms (in the English edition of John Napier's Description of the Admirable Table of Logarithmes (S. Waterson, London 1618), Appendix, at p. 4 (Google)). (An explanation of the sign is given in William Forster's Forster's Arithmetick (1673), at pp. 43-44 and pp. 113-14 (Google).) Hence there is an historical association between Exponentiation and this $\times$ usage which some readers may want to understand. I find some explanations in F. Cajori's History of Mathematics (Macmillan, New York/London 1919), at pp. 157-58 (Internet Archive). Perhaps the pedagogic example is the better for being elementary? Eebahgum (talk) 18:38, 9 January 2023 (UTC)

I adjusted the intro to be consistent with /times. I left the rest of the article as is. Emschorsch (talk) 04:49, 24 July 2023 (UTC)