In this chapter we introduce three number systems: the real numbers, the inte-gers and the rationals.
Here is an infinite straight line: . . . . . .
Choose a point on this line and label it as 0. Also choose a unit of length,and use it to mark off evenly spaced points on the line, labelled by the wholenumbers . . . ,−2,−1,0,1,2, . . . like this: 0 1 2 3-1-2-3
. . .. . .