And we could go the other way. If we are at a local minimum point at x equals c, or relative minimum point, so our first derivative should still be equal to zero, because our slope of a tangent line right over there is still zero, so f prime of c is equal to zero. But in this second situation, we are concave upwards. The slope is constantly increasing. We have an upward opening bowl. And so here, we have a relative minimum value. Or we could say our second derivative is greater than zero.