Showing posts with label generality. Show all posts
Showing posts with label generality. Show all posts

Wednesday, 9 April 2008

Generality and Specificity

Shifting from the general to the specific and vice-versa is integral to working mathematically. It is what allows us to talk of infinity starting from simplicity. For example when talking of the commutativity of addition of the real numbers...I can specify an example:

1 + 2 = 2 + 1

but I can also speak generally and say that:

a + b = b + a
...for a,b R (member of the real numbers)

This demonstrates specifying an example and then conjecturing a generality to be tested based on that example.

Task: Think about when you have worked mathematically, something which you couldn't do immediately, that posed a difficulty. What was your process at first? How did you attack the problem? How did you make it more manageable? How did you complexify? Did you extend? Think about how you can relate what you did to generalising and specifying.

Thinking about how we function in this case allows us to identify key moments and processes that if worked on can be used as tools for dealing with mathematical problems.

Tuesday, 8 April 2008

Things to do with 11...

Some folks may recognise these 2 problems/tasks/puzzles as they are lifted quite unashamedly from the excellent Thinking Mathematically by John Mason. They both relate to 11 and its multiples.

Working with these problems myself and with others has served to highlight:

(i) an awareness (or lack) of our number system and how it is built up but also,
(ii) a need to function generally whilst working with specifics i.e. proving that all multiples of 11 demonstrate a certain property.

The first of the problems looks at 4 digit palindromes and the fact that they are all divisible by 11, can you show this? An example of a palindrome would be

racecar, hannah, I

What would a numeric palindrome look like?

The second of the problems asks why the test for divisibility by 11 works...for those who aren't sure this is as follows:

Add up the even digits, add up the odd digits, find the difference.
If the difference is divisible by 11 so is the original number

e.g. 174757
odd digits --> 1 + 4 + 5 = 10
even digits --> 7 + 7 + 7 = 21
Difference is 11 so our number should be divisible by 11

The question remains why does this work? Can you show this in general?