마스터프렙 No.1 유학생 전문 인터넷 강의 사이트

COMMUNITY


Title	[Mia So] A Question about Concavity
	AP Pre Calculus		6
Author	tol***	Date Posted	2023-12-30 오전 10:55:11
Dear Mia So, Hello. I am writing to you to ask you something about concavity. When you were explaining "Positive and decreasing," you explained that it looked a little bit like half a downward smiley face/sad face. You explained that it looked like the left half of the sad face. However, when you explained positive and decreasing on the 4th question of the AP Style problems, you then changed the explanation and said that 'positive and decreasing' looks like the right half of the sad face. Based on your explanations, wouldn't the right half od the sad face be "negative and decreasing"? Please let me know. Thank you. Sincerely, Doyun
2023-12-31 오후 10:26:47 Hi Good Question! To solve this problem, you need to identify the 'subject'. That is; 'WHAT' is positive and decreasing in this problem? Is it just 'F' or 'rate of F'? When we have a graph looks like the left half of the sad face(below sketch), THE RATE OF f is positive and decreasing. (not f is positive and decreasing) For number 4, the question is asking where F is positive and decreasing, so we need to find where F is positive (= above the x axis) and F is decreasing(=goes down). On the other hand, For number 3(previous question), the question is asking where RATE of T is positive and decreasing, so we need to find where the RATE of T is positive (= slope of T is positive = goes up) and RATE of T is decreasing (=concave down = sad face). I hope you understand now :)