05.04.2013 Views

history of mathematics - National STEM Centre

history of mathematics - National STEM Centre

history of mathematics - National STEM Centre

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

12 Summaries and exercises<br />

• extending the number line to include complex numbers (Activity 11.3)<br />

• looking at an axiomatic approach (Activities 11.5 to 11.7)<br />

• Boolean algebra as an example <strong>of</strong> an axiomatic system (Activity 11.8)<br />

• exploring Clifford algebra (Activities 11.9 to 11.14)<br />

• generalising beyond numbers (Activity 11.15).<br />

Practice exercises<br />

1 In his Arithmetica infinitorum, John Wallis gives his view that a number larger<br />

than infinity can be found.<br />

I<br />

a ratio greater than infinity such as a positive number may be supposed to<br />

have to a negative number<br />

a Investigate the sequence <strong>of</strong> positive ratios — — — —. This is a sequence <strong>of</strong> the<br />

form — with n increasing. In numerical terms is the sequence descending or<br />

n<br />

ascending?<br />

b Now investigate the sequence <strong>of</strong> ratios — where n is any positive number. What<br />

n<br />

can you say about the sequence as n tends towards zero? Draw a graph using n as<br />

the horizontal axis.<br />

c By extending the sequence to negative values <strong>of</strong> n, again with n decreasing, can<br />

you explain why John Wallis may have put forward the view expressed?<br />

d What is wrong with Wallis's argument?<br />

2 In the book Mathematical thought from ancient to modern times, Kline assigns<br />

to Augustus de Morgan the following:<br />

The imaginary expression -^(-a) and the negative expression -b have<br />

this resemblance, that either <strong>of</strong> them occurring as the solution <strong>of</strong> a<br />

problem indicates some inconsistency or absurdity. De Morgan illustrated<br />

this by means <strong>of</strong> a problem. A father is 56; his son is 29. When will the<br />

father be twice as old as the son?<br />

a Solve de Morgan's problem by setting up an equation to find out how many<br />

years from now the father will be twice as old as the son.<br />

b In what way does your solution support de Morgan's claim?<br />

c How do you interpret your solution and what assumptions are you making about<br />

numbers?<br />

d How can de Morgan's original question be phrased so that the solution no longer<br />

appears absurd?<br />

3 Discuss critically various contradictory beliefs which have been held about<br />

negative numbers throughout the centuries and throughout the world.<br />

757

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!