I'm having trouble thinking about the second derivative. I've been thinking of it as the rate of change of the rate of change, but that seems to have gotten me into some trouble. This is a quiz question that I had: http://i.imgur.com/WUMqY5C.jpg Ignore the first part, as it should read f' < 0. This leaves only point A and B. I chose B since although the rate of change is negative, it's not accelerating or decelerating. It looks to be remaining rather constant. I think the correct answer is A, which doesn't make sense to me - the rate of change is decreasing, but it's decreasing faster and faster around the A point. Can someone help me understand this concept?