Given f '(x) = (5 - x)(8 - x), determine the intervals on which f(x) is increasing or decreasing. (2 points)

Decreasing (-∞, 5); increasing on (8, ∞)
Increasing (-∞, -5) U (-8, ∞); increasing on (-5, -8)
Decreasing (5, 8); increasing on (-∞, 5) U (8, ∞)
Decreasing (-∞, 5) U (8, ∞); increasing on (5, 8)
I think it's B

@3mar do you think you could help me?

Question

Given f '(x) = (5 - x)(8 - x), determine the intervals on which f(x) is increasing or decreasing. (2 points)
 		
	Decreasing (-∞, 5); increasing on (8, ∞)
	Increasing (-∞, -5) U (-8, ∞); increasing on (-5, -8)
	Decreasing (5, 8); increasing on (-∞, 5) U (8, ∞)
	Decreasing (-∞, 5) U (8, ∞); increasing on (5, 8)
I think it's B

@3mar do you think you could help me?

3mar · Answer

Yes, In Sha' Allah..
.
Are you familiar with that?
Critical points of f are when f'(x)=0 or when f'(x) is undefined
f'(x) > 0 f(x) is increasing
f'(x) < 0 f(x) is decreasing

volpina · Answer

okay, thanks, could you please help me with some more?

3mar · Answer

So Did you get the idea?

or need some more details?

volpina · Answer

I got the idea :)

3mar · Answer

I am happy to hear that.
If there are any more questions, pleasure is mine to help!

volpina · Answer

yay! i'll open a new question