Times

Saturday 22 October 2005 at 9:17 pm | In Articles | 6 Comments

Along with other British mathematicians I am very lax about how I write the multiplication symbol. I will write

    \1 \times 2 \
1.2 \
1 \cdot 2

and then maintain that the context will tell the reader what is meant.

The problem comes from the fact that:
1. British students aren’t used to using the dot as a multiplication symbol – it doesn’t seem to be used in schools. They only want to use \times

2. The international students have never used \times (though it appears on their calculators which seem to be designed for the American market) and they are much more careful with the dot which must be on the centre of the line. They also are unhappy about the British habit of not worrying where the decimal point goes: 1.2 or 1 \cdot 2

The students love to tell me off for using the ‘wrong’ symbol on the grounds that whatever I do is wrong 8-) It makes for very interesting discussions about the international differences in mathematics and led to a wonderful note from some of the students:

    If I insist on using . for multiplication then asking them to do Q.1 on p.77 should be read as Q \times 1 \text{ on } p \times 77 :-?

It’s nice to leave a class with a smile on my face.

PS For many years British students have used the word ‘times’ as in times by 3 or even worse ‘timesing’. It sounds horrible to me but I seem to have lost the battle to say ‘multiply’

6 Comments »

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  1. If I recall correctly, the multiplication symbol is written as \times in China as well, at least for grade school mathematics.

    Personally, I like the \cdot notation better, since with the handwriting of many people nowadays times is indistinguishable from x, or even y for some people.

    Comment by Wing — Sunday 23 October 2005 12:08 am #

  2. Do the people who use \times for multiplication also use it for dot products?

    Comment by Tom — Sunday 23 October 2005 12:49 am #

  3. By the time the students get to vectors (not reached until near the end of the second year of A level) they have been browbeaten by me to stop using \times. The coefficients in the binomial theorem, particularly with fractional powers, usually makes the point.

    Unfortunately, vector product isn’t in the syllabus, which would be fun!

    Comment by Steve — Sunday 23 October 2005 10:57 am #

  4. Wait, so do ya’ll across the pond use \times for dot products? Because the way I learned it, \times is the cross product and \cdot is the dot product.

    Comment by Wing — Wednesday 26 October 2005 4:55 am #

  5. In singapore, the students are taught to use the \times symbol. Although, at secondary level (age 13-16), if they learn algebra, the \cdot symbol is used to avoid confusion with x.

    Comment by tpc — Wednesday 2 November 2005 1:16 am #

  6. In the UK, in my school (Alevel) my teacher always uses the \cdot notation after GCSE.

    Comment by William — Friday 31 March 2006 3:37 pm #

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