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? Well, in order to do the second derivative test, you have to figure out what the second derivative is, so let's do that. V prime prime of x is going to be equal to, is going to be equal to 24x, 24 times x to the first, minus 200. Minus, minus 200. And you can just look at inspection that this number right over here is less than four, so this thing right over here is going to be less than 100. You subtract, you subtract 200, so we can write the second derivative at 3.92 is going to be less than zero. You can figure out what the exact value is if you like.