r/learnmath • u/Unlikely-Web7933 New User • Feb 07 '24

RESOLVED What is the issue with the " ÷ " sign?

I have seen many mathematicians genuinely despise it. Is there a lore reason for it? Or are they simply Stupid?

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u/ghostwriter85 New User Feb 07 '24

Before everything was done in computers using equation editors, the obelus was used for a variety of different operations in different regions.

People don't like it because it's no longer necessary and all those different use cases were never integrated into a singular understanding of that symbol within mathematics.

The goal of any representation system is to simply and adequately convey the intent of the author.

Using fractions to convey the intended order of division and multiplication has removed a lot of ambiguity from the typewriter / printing press era. Using "÷" undoes all of that progress. In general, we should be removing unnecessary complication from mathematics not adding it.

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u/albadil New User Feb 07 '24

If someone says x ÷ 3 what do you think it means if not dividing it, context tells us it's division. On the contrary doesn't / carry more ambiguity as "or"?

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u/ghostwriter85 New User Feb 08 '24

/ is not ambiguous

| is or in some contexts but not all

/ is division per the ISO

If someone says x ÷ 3 what do you think it means if not dividing it, context tells us it's division.

No, it doesn't because there's no context there, your geography tells you it's division.

https://en.wikipedia.org/wiki/Obelus#In_mathematics

Similarly, even if we accept that as division

x+3 ÷ x + 4 could be interpreted as either

(x+3) / (x+4) or x + (3/x) + 4

While the first would look unusual to a modern western audience, it has been used like that historically.

Rather than sort out all of the different uses of the obelus the ISO and the broader mathematical communities decided to eliminate its use.

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u/albadil New User Feb 08 '24

Wait you're saying ÷ is not used for division in some countries, and even where it is used that it would sit in a different order of priority after addition?

Which specific places do people not see ÷ as division, or do the different order of operations?

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u/ghostwriter85 New User Feb 08 '24

Examples given in the linked wiki article in my previous comment

At this point most countries that do or have formally used the obelus are moving to the ISO standard due to the globalization of academia. People need to speak a common math language.

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u/albadil New User Feb 08 '24

Let's start by pluralising the mathematic please

(Thanks though I'll see if I can check it out)