Or we could say our second derivative is greater than zero. Visually, we see it's a relative minimum value, and we can tell just looking at our derivatives, at least the way I've drawn it, first derivative is equal to zero, and we are concave upwards. Second derivative is greater than zero. And so this intuition that we hopefully just built up is what the second derivative test tells us. So it says, hey, look, if we're dealing with some function f, let's say it's a twice-differentiable function, so that means that over some interval, so that means that you could find its first and second derivatives are defined. And so let's say there's some point, x equals c, where its first derivative is equal to zero. So the slope of the tangent line is equal to zero.