ABSTRACT
Figure 4.1 The number line (showing positive and negative integers)
When we are performing arithmetic using numbers we do need to be careful when we show the signs. For example, if we need to find the sum of the first three positive integers (1, 2, and 3) we would write this as follows:
Sum of first three positive integers:
1 + 2 + 3 = 6
However, if we are asked to find the sum of the first three negative integers (−1, −2, and −3) we would write:
Sum of first three negative integers:
(−1) + (−2) + (−3) = −1−2−3 = −6
Notice how we have used brackets to help to clarify the arithmetic. Brackets can be very useful as we shall see a little later on. Because we frequently have to deal with numbers that lie between two integer numbers, integers are often not precise enough for use in engineering applications. We can get over this problem in two ways; using fractions and using a decimal point. For example, the number that sits mid-way between the positive integers 3 and 4 can be expressed as 3½ or 3.5. Similarly, the number that sits equally between −1 and −2 can be expressed as −1½ or −1.5 (see Fig. 4.2). A table of some common fractions and their corresponding decimal values is shown in Table 4.1. Laws of signs
There are four basic laws for using signs. They are:
Positive whole numbers are called positive integers whilst negative whole numbers are called negative integers.
