Talk:Multiplication

Middle dot vs. period

The middle dot is standard in the United States, the United Kingdom, and other countries where the period is used as a decimal point

Well, from my experience it's not true. Back in Poland, since the primary school, I'd been, like everyone else, taught to use the middle dot. We use the comma as the decimal mark. Now I study at an English university and it's English lecturers who use the period as the multiplication symbol. I had not even known the period could be used like this before I came here. So it doesn't look like the middle dot is standard in the UK. Ustt (talk) 12:05, 27 November 2013 (UTC)

I went to school in Hungary. We never, in no circumstances use low period to denote multiplication. Middle dot is taught for multiplication sign. Alternatively, no sign between numbers and variable letters, or two variable letters, means multiplication. The × cross is used outside maths and physics literature. We understand period as a thousands separator although the official thousands separator is whitespace, so printed media would use whitespaces, not points. Decimal point is comma. Dot as decimal point is only accepted or used in computing in Hungary. --2A00:1028:8386:EC12:D8EE:B92:42E2:11F5 (talk) 10:02, 8 January 2021 (UTC)

I've updated the page. The documented behavior (middle dot as decimal) is archaic, but still seen in some older journals and eg the history dept of cambridge university. See Interpunct and Decimal Separator for more info, but the TLDR is, the UK is not out of step with the rest of the planet on this: since 1968 we use the SI system, which mandates either a period or a comma as the decimal separator. --207.191.44.146 (talk) 18:29, 5 November 2021 (UTC)

Saltire

Why is the x figure called a cross? This is not what the lay person thinks of when reading the word cross. Technically, I guess it is a saltire, but that word's is too arcane (Wikipedia even marks it as wrong as I write it). Is "ecks" really not what it is? Certainly as kids learning multiplication we considered it "ecks"/"ex".211.225.33.104 (talk) 09:33, 9 July 2014 (UTC)

I like the idea of calling it a saltire, though I don't usually think of a saltire as crossing at a 90° angle. Unschool 07:28, 10 November 2015 (UTC)

When you need to distinguish the letter x from the operator ×, it is a bad idea to call × an ex, ecks, x figure or such. It _actually_ is a cross. A special kind of cross. If you want to specify which cross it is then say, the multiplication sign. Saltire is a word that calls for a dictionary. --2A00:1028:8386:EC12:D8EE:B92:42E2:11F5 (talk) 09:46, 8 January 2021 (UTC)

"Multiplikand" listed at Redirects for discussion

A discussion is taking place to address the redirect Multiplikand. The discussion will occur at Wikipedia:Redirects for discussion/Log/2021 April 9#Multiplikand until a consensus is reached, and readers of this page are welcome to contribute to the discussion. Regards, SONIC⁶⁷⁸ 00:00, 9 April 2021 (UTC)

"Multiplikator" listed at Redirects for discussion

A discussion is taking place to address the redirect Multiplikator. The discussion will occur at Wikipedia:Redirects for discussion/Log/2021 April 9#Multiplikator until a consensus is reached, and readers of this page are welcome to contribute to the discussion. Regards, SONIC⁶⁷⁸ 00:00, 9 April 2021 (UTC)

In the history of methods of finding products

the method noted as used in Germany (and often used now in the US) is also found in George Berkeley’s Arithmetica (1707) - was this amongst its first appearances in an English text? ELSchissel (talk) 02:04, 25 March 2022 (UTC)

(though I am reminded now that the Berkeley book was written in Latin. Hrm.) ELSchissel (talk) 02:06, 25 March 2022 (UTC)

Defining the product of real numbers

I never learned TeX or LaTeX, so perhaps the following critique of the section Multiplication § Product of two real numbers is way off base but, if I've misunderstood it, a clarification is surely needed to accommodate readers like me.

The claim, as I understand it, is:

If the real number a is the least upper bound of a set A of rational numbers and the real number b is the least upper bound of a set B of rational numbers, then their product a⋅b is the least upper bound of the set C of rational numbers that consists of all the products of a rational number in A and a rational number in B.

However, if A contains a negative number such as −1 and B is not bounded below, then the set C will not be bounded above; it will have no upper bounds and hence no least one.

What am I missing? Peter Brown (talk) 03:37, 7 February 2023 (UTC)

Good catch. The previous text omitted to say that a and b were supposed positive. I have rewritten the section for fixing this and making the link with infinite decimals. D.Lazard (talk) 17:06, 7 February 2023 (UTC)

Got it! Thanks.Peter Brown (talk) 17:27, 7 February 2023 (UTC)

Merging new section with "Multiplication of Different Kinds of Numbers"

A recent large contribution (16:33, 15 October 2022‎ by Fgnievinski) introduced an unreferenced section ('Definitions') near the top of the article. It contained useful text but as far as formal definitions go it seemed ad-hoc and not fundamental enough. e.g. the 'Integers' subsection rested on a fait-accompli matrix rather than the defining laws leading to that matrix, i.e. the definition behind the result.

Elsewhere the Multiplication article has more authoritative language and cites Peano etc.; we could go even further and cite Artin or Ireland or other authors of adult books (not high school intro texts) covering arithmetic. But meanwhile I'll merge this uncited content with 'Multiplication of different kinds of numbers', to aid the older section's introductions. Mebden (talk) 13:45, 24 September 2023 (UTC)

@D.Lazard: you reverted this edit so I have introduced just now a compensatory flag to the Definition section indicating its problems. I think it would be a pity to lose the current Definitions text in any coming expert rewrite as the text might help with intuitive understanding nonetheless. But it doesn't belong anywhere near a Definitions section. Mebden (talk) 13:58, 25 September 2023 (UTC)

I agree that section § Definitions is poorly written, and this is the reason for which I have not removed the template, although I would have used another template, such as {{cleanup}}.

However, there is a large overlap between this article and Product (mathematics) and there is no valid reason for this WP:REDUNDANTFORK, as both articles are very elementary. This should be fixed, and a WP:MERGE seems the only reasonable solution. Indeed, most readers of these elementary article do not have a clear notion on the difference between a multiplication and a product. Thus, they would come at random to either article. D.Lazard (talk) 17:41, 25 September 2023 (UTC)

Wiki Education assignment: 4A Wikipedia Assignment

This article was the subject of a Wiki Education Foundation-supported course assignment, between 12 February 2024 and 14 June 2024. Further details are available on the course page. Student editor(s): Not Fidel (article contribs). Peer reviewers: Ahlluhn.

— Assignment last updated by Ahlluhn (talk) 00:57, 31 May 2024 (UTC)

Definition in Natural Numbers

The summation definition in the natural numbers is incomplete. The case when r=1 needs to be included. 75.191.107.254 (talk) 13:09, 27 April 2024 (UTC)

It is included, as ${\textstyle \sum _{j=1}^{r}s=\underbrace {s+s+\cdots +s} _{r{\text{ times}}}}$ reduces, when r = 1, to ${\textstyle \sum _{j=1}^{1}s=\underbrace {s+s+\cdots +s} _{1{\text{ times}}}=s.}$ This is included in the definition of capital-sigma notation. D.Lazard (talk) 13:39, 27 April 2024 (UTC)

Multiplier and multiplicand

I find the naming of factors slightly inconsistent. The example expression 3×4 is phrased as “3 multiplied by 4”, but then the next paragraph talks about “3 (the multiplier) and 4 (the multiplicand)”. If 3 is “multiplied by” 4, the corresponding active voice would read: “4 multiplies 3”, which sounds like 4 should be the multiplier (thanks to its agent suffix) and 3 should be the multiplicand (thanks to its operand suffix), i.e. the quantity that is operated on.

This question may have some real-world consequences, as illustrated by this LinkedIn post: https://www.linkedin.com/posts/nemanja-mileti%C4%87-4209311a1_i-found-this-problem-on-linkedin-and-it-was-activity-7265048840594968576-wgGu Petr.Tesařík (talk) 07:57, 27 November 2024 (UTC)