Our derivative is another polynomial. It is defined for all real numbers. So these are our two critical, our critical points, or we could even say critical values. So let's think about what g prime is doing on either side of these critical values. And I'll draw a little number line here to help us visualize this. And so, so there we go, a little bit of a number line. And let's see, we care about zero, and we care about four fifths.