If an equation can be rearranged into the form \(y = mx + c\), then its graph will be a straight line. In the above: \(x + y = 3\) can be rearranged as \(y = 3 - x\) (which can be re-written as ...

To work out the equation of a line from a graph, find the gradient and the \(y\)-intercept. The gradient is the same all along the line, so it doesn’t really matter where you start or finish ...