5.2 Negative Numbers

It took mathematicians a long time to come to terms with negative numbers, so do not be surprised if you need to work slowly and carefully through this section.

In Unit 2 we looked at how to show numbers using number lines, which looked a little like this:

Of course, the natural numbers, positive whole numbers, are not sufficient to describe the world around us. Think about going to the grocery store and the various prices you see. You have learned about zero, fractions, decimals, and maybe even pi before. pi, pronounced “pie,” is approximately 3.14. You will learn more about this interesting number in Unit 10 when studying circles. To put pi on a number line looks like this:

Now, we extend the number line to the left, to add in the negative numbers, which are used when you want to describe a quantity that is less than zero. That number line looks like:

Pencast symbol For more on the number line and negative numbers take a look at this pencast. (Click on “View document.”)

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Can you think of a number line that you use that has negative numbers? How about a thermometer? For example, on a cold winter morning, your thermometer might read “4 ºF.” This number is read as “negative 4 degrees Fahrenheit”  or “ minus 4 degrees Fahrenheit,” and it means 4 degrees below zero. Brrr!

5.1.8 Prefixes in the Metric System

5.2.1 Negative Numbers on a Thermometer