Re: decimal point/comma (was conplaneteering)

On 20 Feb 2005, at 9.14 am, Carsten Becker wrote:

> On Friday 18 February 2005 14:44 +0100, Mark J. Reed wrote:
>
> > But in typeset mathematics books long before computers,
> > multiplication was indicated by either simple
> > juxtaposition or a dot.  As I said, I've personally never
> > seen × and ÷ anywhere other than in early-grade workbooks
> > and on calculator keys.
Although the most advanced maths I've done is first year Uni, I think
I'm inclined to say that I've seen the cross for multiplication (among
other mathematical functions) more frequently that 'early-grade
workbooks'. Certainly it disappears in frequency by the time you
introduce pronumbers, but it's definitely used. Writing 2(3x), for
instance, without the brackets (and without expanding it for whatever
reason), would be 2 × 3x. I suspect this is because in handwriting, 2 ·
3x could be mistaken for 2.3x, whereas 2 × 3x is unambiguous (most
Australian people doing maths that I've come across use a cursive x,
not a print x, so it's obviously different---perhaps *so* it's
obviously different; but a print x looks as bad to me in handwriting as
a roman x looks in print). (I specify Australian people because some of
my tutors at Uni who had non-Aussie accents use a print x, so perhaps
the cursive x I'm familiar with is not a universalism---it's basically
a backwards c and a forwards c joined together. Used by people who
would never otherwise write in cursive.)

In print, I'd hazard that middot and cross times-symbols are of similar
frequency, but in handwriting the cross is more common. But that's just
my experience, and as I said it only extends to first year uni maths.

> The Maths textbooks I had have always been using + - ·
> (middot) and : for addition, substraction, multiplication
> and division. Fractions are written as
Colon for division? That seems odd. I spose, tho, that a frequency of
1:2 (one in two) means that 1/2 (one on two; a half) of them are that,
so it makes sense too... Never seen it tho; it's always been for ratios
etc. IME.

(Incidentally, you shouldn't really be using - for minus... once we're
venturing outside of ASCII, you might as well use the proper minus
sign, -. It looks better against + × · ÷ etc.)

>  a
> ---
>  b
>
> Since we've been dealing with algebra, you can of course
> omit the · sign in unambiguous environments, i.e. between
> brackets or variables.
Of course. As well as constants :) (360° is 2π rad, but π, I hope, is
not a variable.)

Incidentally, when I was first taught about radians, we (and our text
book) used a symbol that looked like a superscripted c, or a degrees
sign with a bit taken out of it. This was in high school. I don't think
we ever used it at Uni, and I searched the Web just now and I can't
seem to see any trace of it. Does such a symbol really exist, or have I
remembered the right glyph for the wrong meaning, or was it merely an
invention of the Victorian Curriculum and Assessment Authority (VCAA)?

--
Tristan.

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