So that is four fifths. And let's just think about what g, what g prime is doing in these intervals. And these critical points are the only places where g prime might switch sides, switch signs. So let's first think about this, let me pick some colors I haven't used yet. So let's think about the interval from negative infinity to zero. So this is the open interval from negative infinity to zero. And we could just plug in a value, we could, let's try negative one.