Graphs are useful for two purposes. The first is to express equations visually, and the second is to display

statistics or data. This section will discuss expressing equations visually.

To a mathematician or an economist, a variable is the name given to a quantity that may assume a range of

values. In the equation of a line presented above, x and y are the variables, with x on the horizontal axis and y

on the vertical axis, and b and m representing factors that determine the shape of the line. To see how this

equation works, consider a numerical example:

In this equation for a specific line, the b term has been set equal to 9 and the m term has been set equal to 3.

Table A1 shows the values of x and y for this given equation. Figure A1 shows this equation, and these values,

in a graph. To construct the table, just plug in a series of different values for x, and then calculate what value of

y results. In the figure, these points are plotted and a line is drawn through them.
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