As I left home in the morning, I put on a light jacket because, although the temperature was dropping, it seemed that the temperature would not go much lower. But I was wrong. Around noon a northerly wind blew up and the temperature began to drop faster and faster. The worst was around 6 pm when, fortunately, the temperature started going back up.
(a) When was there a critical point in the graph of temperature as a function of time?
(b) When was there an inflection point in the graph of temperature as a function of time?