# Talk:Formula

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We need a WikiChem language to write chemical formulae, similarly to WikiMath - unsigned

Is this a disambiguation page? It has the template and the alternate meanings, but what the heck? It seems like it was written by a high-school Chemestry teacher or something. Eww. Who wrote this? Is anyone going to step in and improve it? I'd rather not intrude, though I guess if I have to eventually... =/ Matt Yeager 06:26, 3 December 2005 (UTC)

The reference to needing integral calculus to determine the volume of a sphere doesn't make sense, in light of Archimedes. While it makes sense to argue that integral calculus is needed to derive a formula with which to determine the volume of a sphere without dunking the sphere in water, one can nonetheless dunk a smaller sphere in water, measure the volume of water displaced, and proportionately calculate the volume of a larger sphere. So, calculus is not needed to determine the volume of any sphere. Its use is limited to creating a general formula with which to calculate a sphere's volume. - unsigned

If you don't have the formula, you do in fact need integral calculus, because otherwise you will encounter experimental error, and you will only come up with a rough approximation. —Preceding unsigned comment added by 68.144.178.98 (talk) 18:56, 15 December 2007 (UTC)

It seems that the word "formula" - even in the limited context of mathematics - has multiple meanings. The basic meaning is akin to "shorthand". The other meaning is like in the conversation: "how do you calculate the volume of a sphere?". Answer: "you may compute the volume using integral calculus, but there is a formula for that". This is probably why the sphere volume formula is included at all in this article. Would it be a suggestion to write a short abstract article on "formulae in mathematics and science", which only says that a formula is a shorthand, and then to expand in separate articles on formulae in mathematics and (most) other sciences, and formulae in chemistry? Rbakels (talk) 12:17, 26 April 2012 (UTC)

Looking at this page, I'm thinking that it could still use a lot of improvement (eg: adding a section on chemical formulae), although it is much better than it was when Matt Yeager made his comment. DonkeyKong the mathematician (in training) 10:34, 22 April 2007 (UTC)

by the way, this page should include the standard units used for the formula. the is what is the unit that we use to measure the r (radius),is it in M, cm or mm? by including the standard can help the readers to understand more easily. —Preceding unsigned comment added by 60.50.152.179 (talk) 08:33, 8 September 2007 (UTC)

The formula $V = \begin{matrix} \frac{4}{3} \end{matrix} \pi r^3$ is independent of the used units. For example, if you insert numbers with r in cm then you get V in cm3 after taking the cube, and if you insert r in mm then you get V in mm3. The same applies to E=mc2 and other physical formulas. You don't replace the variable with a number only. You replace it with a number and unit of your choice, and the unit is included in the operations. When geometry is not applied to the physical world, it is common to not use units for length, area, volume. For example, the radius of a circle may simply be given as 1 and it's area as π. This may assume some underlying coordinate system. PrimeHunter 15:13, 8 September 2007 (UTC)

The disambiguation page says: "See [formula] for an account of the concept in mathematics and the sciences". I think this is a good description of what this page seems to be trying to achieve, and so perhaps it should be renamed to reflect this. DonkeyKong the mathematician (in training) 19:38, 28 April 2007 (UTC)

Beware though that chemistry is a branch of science that uses formulae in an entirely different way (e.g. structure formulae). Rbakels (talk) 12:08, 26 April 2012 (UTC)

i think that wikipedia should be a place where people can't edit material. it's not right. people come here for help and what they read is usually not true and weird. —Preceding unsigned comment added by 68.62.102.249 (talk) 02:08, 13 September 2007 (UTC)

This is not the place to discuss who can edit. Have you found an error in formula? PrimeHunter 03:04, 13 September 2007 (UTC)

## Plural

'Formulas' is not the plural of 'formula' in this world or the next! Please, for the sake of the children, don't use it. Falcifer 14:46, 5 June 2007 (UTC)

Both forms are usually considered right in English and this is the English Wikipedia. See for example http://mw1.merriam-webster.com/dictionary/formula. Google shows 'formulas' is more common than 'formulae', and I'm guessing the difference is increasing. 36 million pages currently disagree with you. PrimeHunter 15:15, 5 June 2007 (UTC)

It doesn't really matter how many pages disagree, but if a Merriam Websters uses it I guess it must be acceptable (probably a case of being incorrect but gradually becoming accepted over time). Richard001 01:20, 25 August 2007 (UTC)

If it becomes sufficiently accepted then I think it also becomes correct (which doesn't have to mean the old form becomes incorrect). MathWorld is referenced in lots of math articles and http://mathworld.wolfram.com/Formula.html says:
The correct Latin plural form of formula is "formulae," although the less pretentious-sounding "formulas" is more commonly used.
The Latin Wikipedia can say formulae but we don't have to. Lots of words with Latin origin are changed in English and other languages. PrimeHunter 02:41, 25 August 2007 (UTC)
I'm reminded of an old commercial where the tag line was, "Stop! You're both right!"
If we're talking about Latin, the correct plural form of formula is indeed "formulae" in the nominative case (subject), but it's "formulas" in the accusative case (object), because "formula" is a first-declension feminine regular noun.
That's where the problem comes from, IMHO. Myself, I have no problem writing both -ae and -as in English technical manuals, depending on whether it's subjective or objective case. But since most words in English are made plural by adding "s" in either case, the momentum among the masses is with "formulas". Kkken (talk) 12:03, 9 January 2009 (UTC)

Stop arguing which one is right. I set new reference for both words. Thanks to Oxford. --Octra Bond (talk) 03:36, 18 February 2011 (UTC)

## Expressions

I fail to see how "formula" is analogous with "expression". You can make an argument for it, but as the article says "In mathematics, a formula is a key to solve an equation with variables." - which means a variable is being solved for by setting it equal to a known expression, i.e. an equation. Not only this, but it is misleading, since typing in "physics formulae" in Google shows pages and pages of equations and no expressions. Mind you, that is just physics, but I can't recall a single formula from either math or physics that is just an expression. I realize that formulas can be inequalities or identities etc... but wouldn't any of these make more sense than expression? —Preceding unsigned comment added by 99.227.12.225 (talk) 22:22, 2 March 2008 (UTC)

Funny thing, I agree with 99.227.12.225 in "failing to see how 'formula' is analogous to 'expression'", but I don't go with "formulas can be inequalities or identities etc." I know you can find dictionaries to support a lot of different definitions, but the way I learned it, there was a hierarchy with nice, clean divisions: an equation and an inequality are statements, and have verbs (equals, doesn't equal, is greater/lesser than); a formula is the string on one side of an equation or inequality (usually the right side), it has one or more operators but no verb, and it's a formula for whatever's on the other side of its equation; an expression might be a parts of a formula, or a whole formula, or just some variables slung together, but again there's one or more operators and no verb; and variables and constants are single characters with no operator or verb.
In that nice, clear division, y=mx+b is an equation, mx+b is the formula for y, and it's also an expression. mx is also an expression. And a/b would also be an expression, one without any assumptions that it refers to anything.
Funny that that's how I learned it, and how well it worked where I did my schoolin' and cipherin', but it clearly isn't universal. Kkken (talk) 12:38, 9 January 2009 (UTC)

There's definitely a problem with the whole "expression" thing, because the article on 'expression' says that it can't contain an equals sign. So a formula, which by definition virtually has to contain an equals sign, must be made of two expressions, one on either side of that sign. i.e. this page currently contradicts the 'expression' page to which it is linked. Could someone with a bit more confidence about the finer points of terminology correct this and/or that page?? —Preceding unsigned comment added by 90.219.248.4 (talk) 09:10, 13 October 2009 (UTC)

A further comment, relating to Kkken's entry: having had to research this for teaching Maths, I think the way Kkken learned it, while it chimes with my own experience, contains just a small misconception (which, really, doesn't matter that much): we often meet formulae as just the 'string on one side of an equation or inequality' etc., such as IR for voltage, or ma for mass, but in both cases the entire formula (or 'recipe') does contain an equals sign: V=IR; F=ma. So although the important part of a formula is generally the RHS, a formula really can be an equation or inequality, and in fact pretty much has to be. If Kken's definition were right, he'd have to accept that a formula is at least a kind of expression (if not analogous with 'expression'), since IR, ma or just mx+c are all expressions.

The difference between equations/inequalities and formulae, as I now understand it, is that although formulae are always equations/inequalities, the reverse does not hold. A statement such as V=15 is not generally true (only works if I = 5 and R = 3, or some other such combination), but is still an equation. A formula, however, must be generally true under certain conditions; hence V=IR is a formula as it works for all combinations of I and R under 'normal' conditions. —Preceding unsigned comment added by 90.219.248.4 (talk) 16:35, 13 October 2009 (UTC)

V=15 is an equation as well: it is an equality that is only true for one or more particular values of the unknown. In this case, solving the equation is almost tautological: the equality is only true if V=15.
I always thought that an expression is a (very) simple form of an equation in the form "unknown = formula not containing the unkown". But I may be wrong. Supposedly equations must be contrasted with identities, relationships between variables that are always true, or at least for a range of values. An equation calls for a solution, an identity doesn't. Rbakels (talk) 07:51, 12 December 2010 (UTC)

## Changing the subject of a formula

This would be a good addition on this page: e.g. The area of a circle (A) is p * r^2. So A = p * r^2 If we know the radius, it is easy to find the area using this formula. However, if we know the area and want to find the radius, rearrange the formula to make 'r' the subject. A = pi * r^2

[Start by dividing both sides by pi] A/pi = r^2

[Then take the square root of both sides]

r = sqrt (A / pi)

Constructive editor (talk) 20:56, 19 February 2009 (UTC)

## Linguistic explanation

As far as I know, the word "formula" is used because it is the Latin deminutive of "forma", I guess because a formula is in essence a shorthand (for something that could have been expressed in ordinary language as well).

I added this comment to the dicussion page rather than the article itself because I am not entirely sure.

Rbakels (talk) 07:42, 12 December 2010 (UTC)