Take a look at the applet: Linear Relations
An equation of the form describes a linear relationship with two variables. The corresponding graph is a straight line. You can find this graph by determining points along this line. This is often done by choosing and calculating the corresponding value for , and by then choosing and calculating the corresponding value for .
Linear equations with two variables such as can be rewritten as a linear function as long as .
For example the equation can be reorganised to give .
This is then a linear function with -intercept and gradient .
: the equation then takes on the form and can be rewritten as . This is a linear function with gradient .
: the equation takes on the form and can be rewritten as . This is not a linear function as there is no gradient. The graph is a line parallel to the -axis.