Extension:
What if we wanted to work out the gradient of a straight line when it is in the form \(ax+by=c\)?
When the line is in the form \(ax+by=c\), notice when both \(a\) and \(b\) are positive the graph is downward sloping (like in our last example). Why? Well, let's convert it to \(y=mx+c\) form to see what's happening with the gradient: