concave up/down? Simplify...using this f(x)=x^3+2x^2-x

jgreen3401

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I was trying to get the complete set of numbers =>< on a concave graph using this f(x)=x^3+2x^2-x.
I was trying to simplify to 3x^2+4x-1 but I'm lost as to where to go next.

If f(x) is negative then slope is down and if it's positive then slope is increasing but there's 2 factors, increasing/decreasing and up and down parabola.

I was trying to attach a picture of the graph but I couldn't figure it out.

So I had X>=-3/2 for all the set of numbers so decreasing slope and facing down.

any ideas?? Thanks for help everyone.

FYI-My vocabulary may be wrong so I apologize.
 
I was trying to get the complete set of numbers =>< on a concave graph using this f(x)=x^3+2x^2-x.
I'm sorry, but I don't know what this means...? Are you saying that you've been given the stated function, and you are needing to find the intervals of concavity?

I was trying to simplify to 3x^2+4x-1 but I'm lost as to where to go next.
Do you mean that you are trying to find the zeroes of the first derivative of the original function, and thus the critical points of the original function? Are you saying that you don't remember how to apply the Quadratic Formula (here) to solve quadratic equations?

...there's 2 factors, increasing/decreasing and up and down parabola.
I'm sorry, but I have no idea what this might mean...?

So I had X>=-3/2 for all the set of numbers so decreasing slope and facing down.
What do you mean when you say that "x > -3/2 for all...numbers"? How can x be greater than a particular value "for all numbers"? How did you "have" this?

When you reply, please include the full and exact text of the exercise, the complete instructions, and a clear listing of your steps so far. Thank you! ;)
 
complete set of numbers

Sorry about that, I had to read this over again but I have find the complete set of numbers for f(x)=x^3+2x^2-x if it's concave.

so that would be down, right?

Would I simplify this to 3x^2+4x-1 then go further or x(x^2+2x-1)

If it doesn't make sense I'm sorry
 
Sorry about that, I had to read this over again but I have find the complete set of numbers for f(x)=x^3+2x^2-x if it's concave.
If what is concave? Concave upward or concave downward? What do you mean by "the complete set of numbers for" the function? Are you saying that the instructions told you to determine if the function had any concavity at all and, if it did, then to determine the domain of the original function? Or something else?

so that would be down, right?
So what would be down? Where? How?

Would I simplify this to 3x^2+4x-1 then go further or x(x^2+2x-1)
Would you simplify what to this first-derivative expression? What more-complicated expression had you obtained? How? Why? How do you somehow obtain the second expression from anything that came before? By what steps? By what reasoning?

What is the full and exact text of the exercise and the complete instructions? What have you done, step by step? What was your reasoning?

I'm sorry, but we really do need you to tell us what you're talking about. That's the only way we can know. Thank you! ;)
 
Sorry about that, I had to read this over again but I have find the complete set of numbers for f(x)=x^3+2x^2-x if it's concave.

so that would be down, right?

Would I simplify this to 3x^2+4x-1 then go further or x(x^2+2x-1)

If it doesn't make sense I'm sorry
Hi,

A lot of people in the USA are used to concave up (concave) and concave down (convex), so when you say concave, they are unsure of just what is meant. BTW: That includes me so I went a googling.

I believe you said (meant) in your initial post consider the function
f(x) = x3 + 2 x2 - x,
asked the question 'When is this function convex, and gave the answer 'The function is convex when x32\displaystyle x\, \ge\, -\frac{3}{2}'. If that were the question and your answer, then you are correct.

I'm unsure of what the other other questions were.
 
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