Before we move on to the other Monkey Rules, let's take a second to talk about Monkey Rule 2. Plotted below is the constant function f[sub]0[/sub](x)=3 and its derivative f[sub]0[/sub]'(x)=0. I've also added the point A to the graph, and a tangent line to f[sub]0[/sub] at A. The tangent line always has slope 0, and so you can barely see it since it coincides with the graph of f[sub]0[/sub]. This is the geometrical reason why the derivative of constant functions is 0. Notice, if you change 3 in the definition of f[sub]0[/sub] to 4 or another constant, nothing changes. This is why Monkey Rule 2 applies to all constant functions. Try it out! Double click on f[sub]0[/sub] and change 3 to another constant. If you set it outside -1 to 4 you won't see it on the graph without adjusting the window.