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Functions

the function f is defined by f(x)=x^3+2x^2-4x+7 for x>-2. Determine showing all the working whether f is an increasing function or a decreasing function or neither.
So I did f'(x) = 3x^2+4x-4
F'(x)>0 so I got x<-2 and x>2/3
F'(x)<0, -2<x<2/3
Since it holds true for both the answer is neither?? I dont understand why the answer is neither. If somebody can explain
Reply 1
Original post by Shas72
the function f is defined by f(x)=x^3+2x^2-4x+7 for x>-2. Determine showing all the working whether f is an increasing function or a decreasing function or neither.
So I did f'(x) = 3x^2+4x-4
F'(x)>0 so I got x<-2 and x>2/3
F'(x)<0, -2<x<2/3
Since it holds true for both the answer is neither?? I dont understand why the answer is neither. If somebody can explain


Yes, it's neither. In your working though you should exclude x<-2.
You can check by sticking it in your calculator or desmos.
(edited 3 years ago)
Reply 2
Original post by mqb2766
Yes, it's neither. In your working though you should exclude x<-2.
You can check by sticking it in your calculator or desmos.

Ok thanks. I got it.

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