## How to use this online book

In the desktop-computer version of this book, icons appear at the top of each page. On other devices, all or some of these icons may also appear.

• Navigation: Navigate between pages using the arrows.

• The table of contents can be toggled on or off using the Contents menu item:

• Words can be searched for using Search button on the menu:

• The font can be changed (e.g., enlarged) using the Font button on the menu:

• A PDF version of the book can be downloaded using the PDF button on the menu:

The book is optimised for online viewing, and the book may be updated frequently, so a printed PDF version may not be the most recent version.

In some places, interactive ‘quiz’ questions are given. In the online version, the background turns from red to green when the answer is correct. Try it now:

1. What is $$1+1$$?
2. What is $$1+2$$?
3. Is $$2 + 2=4$$?