Daily Archives: May 11, 2015

Negative Numbers

What Are Negative Numbers?

Today I was watching the weather report on TV. It said the high for today will be 0 degrees Celsius. It also told me that the high yesterday was 6 degrees above zero or+6 and that tomorrow the high will only be 6 degrees below zero or -6. You are probably familiar with such reports and may even have a thermometer outside that you can read yourself.

But why did the weatherman on TV say plus 6 and minus 6 instead of just saying 6? The high yesterday was just as many degrees away from zero by 6 degrees as the high tomorrow will be away from zero by 6 degrees. We can’t just say the value of the distance from zero but we have also to say the direction away from zero, plus or minus, or with symbols, + or -. Numbers with a sign of + are called positive numbers and numbers with a sign of – are called negative numbers.

Until now, numbers for us have been adequately represented by their value. Now we have to add a new property of numbers and that is called sign. We also now want to be a bit more precise and qualify the value of a number as its absolute value. The idea of absolute value is important in computer programming and higher mathematics but not so much for us now.

A Few Things About Signs

When used to denote the sign of a number the symbols {+.-} are acting as operators. They have only one operand however, and are therefor called unary operators.

Further we have another unary operator,, the absolute value symbol, “| “, that operates on a number to give just its value without any sign. An example is the expression | -6= 6.

You may have noticed that all the numbers we have used until now have shown no sign. Since most numbers we use are positive numbers, by convention, that means by agreement by most mathematicians, we don’t write the + sign for positive numbers. After all, we are mathematicians and don’t like extra writing. This causes a bit of possible confusion when we use the absolute value operator. We have to remember that the expression above is meant as it is written and does not stand for | -6= +6.

Updating the Number Line

Addition and Subtraction of Negative Integers

Multiplication and Division of Negative Integers

Integers

What Are Integers?

The numbers that we made in Introduction to Numbers are called integers or whole numbers. In that section we counted our cats. The numbers we made counted whole cats since we don’t have any partial cats – say a half of a cat – walking around. We also have pies in our house, but someone keeps eating pieces of the pies. We can’t count our pies because we do have half pies in the cupboard. We therefore need some way to count parts of pies and we will explore these ways later in Fractions and

The Integers (Whole Numbers) and the Number Line

  1. counting cats and pies.
  2. The numbers we have talked about are the numbers {0,1,2,…,10,11,12,…,20,21,22,…} these are called integers or whole numbers. Supposing you had half a pie left from supper. What kind of a number would a mathematician use to represent half a pie? We will find out later, but if our integers represent pies, the number to represent half a pie isn’t among them. Hence the integers represent the numbers of whole pies or whole numbers.
  3. Take a ruler marked in centimeters, draw a line from one end of the ruler on the left  to the other and mark on it the integers shown up to 10.
  4. The first thing you may notice is that there is no number at the beginning of the ruler which is the first mark on the ruler. This is actually the number 0.
  5. The next thing you may notice is that between any two numbers on the ruler there are 9 marks in between. We will talk about their meaning later.
  6. Depending on the length of the ruler, the line you draw may allow up t0 30 marks that are numbered and evenly spaced. Longer rulers would allow us to mark more numbers on a longer number line. To be able to mark 1,000 on the number line, we would need a ruler possibly longer than the room you are in. Another characteristic of mathematicians I forgot to tell you is that big numbers don’t scare them. In fact some get excited over the size of really, really big numbers that they invent.

Addition and Subtraction of Integers

Multiplication and Division of Integers

Comparison of Integers

Key Points

A number has the following properties:

  1. It has a representation consisting of the ten digits.
  2. It represents a quantity or value.
  3. The position of each digit in the number is a place value with a distinct name.

Fractions

Fractions

This section deals with situations where we want to represent part of a whole. In an Introduction to Numbers, we suggested that we do not want to represent a part cat but would want to represent a piece of a pie by some number or numerical expression. We discuss how to do this below.

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