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 ...

therefore the bigger the gradient the steeper the line is. A positive gradient is a straight line which slopes up to the right. A negative gradient is a straight line which slopes down to the right.