Now which of these can I use? Well, 12, x equals 12.74 is outside of our, outside of our valid values for x. If x was equal to 12.74, we would cut past, we would completely cut past, the x's would start to overlap with each other. So x cannot be 12.74. So we get a critical point at x is equal to 3.92. And you could look at the graph, and you could say, oh look, that looks like a maximum value. But if you didn't have the graph at your disposal, you can then do the second derivative test and say, hey, are we concave upwards or concave downwards when x is equal to 3.92?