Question

Below is the graph of f ′(x), the derivative of f(x), and has x-intercepts at x = –3, x = 1 and x = 2. There are horizontal tangents at x = –1.5 and x = 1.5. Which of the following statements is true?
A) f has a relative minimum at x = 1.5
B) f has relative maximum at x = -1.5
C) f is decreasing on the interval from x = 1 to x = 2
D) none of these are true
https://seminole.flvs.net/webdav/assessment_images/educator_apcalcab_v14/08_01_04.gif

Answer 1

the derivitive is just the slope

minimum happens when the derivitive goes from negative to positive, imagine a slope of the function, the minimum is where the slope goes from neative to positive, and to get there, it has to pass through 0

max happens when the derivitive goes from positive to negative

increaseing is when the derivitive is positive



so, based on what you said, the slope of f(x) is 0 at x=-3, x=1 and x=2 since those are where the derivitive is 0 (derivitive is just the slope)

A and B are wrong because the derivitive isn't 0 at those points

C is correct because increasing means that the derivitive is positive, and so therefo since the only hoirontal place in between 1 and 2 is 1.5, it must remain positive throughout and not dip down, C is right

D is wrong then




answer is C