ABSTRACT
At the end of this chapter, you should be able to:
• understand rectangular axes, scales and co-ordinates • plot given co-ordinates and draw the best straight line graph • determine the gradient of a straight line graph • estimate the vertical-axis intercept • state the equation of a straight line graph • plot straight line graphs involving practical engineering examples
A graph is a pictorial representation of information showing how one quantity varies with another related quantity. The most common method of showing a relationship between two sets of data is to use Cartesian (named after Descartes∗) or rectangular axes as shown in Fig. 28.1. The points on a graph are called co-ordinates. Point A in Fig. 28.1 has the co-ordinates (3, 2), i.e. 3 units in the x direction and 2 units in the y direction. Similarly, point B has co-ordinates (−4, 3) and C has co-ordinates (−3,−2). The origin has co-ordinates (0, 0).
