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A critical numbers problem

  • #1
find the critical number of the function

f(X)= x^3 + 3x^2-24x

f'(X)= 3x^2 + 6x -24

what do i do, next i found the derivative of the function
 

Answers and Replies

  • #2
arildno
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Well, perhaps you should find out either where the derivative equals 23.67, -17 or perhaps some more important value, say 0.
 
  • #3
ok so its supposed to equal zero as the definition states for critical numbers,

so i just plug in any numbers in the x's
 
  • #4
arildno
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so i just plug in any numbers in the x's
Eeh??
Do you know what an equation is, and how to solve it??
 
  • #5
i think ido, can u show me an example
 
  • #6
yes i know what an equation is, but how do i solve it
 
  • #7
hage567
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Can you name what type of equation that is?
 
  • #8
well im on the section maximum and minum values, it doesnt say what kind of equation it is, id say its a critical number equation
 
  • #9
hage567
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well im on the section maximum and minum values, it doesnt say what kind of equation it is, id say its a critical number equation
:confused: :confused:

Just look at its form. It's a QUADRATIC equation! Have you not learned about those before? There's a formula for finding the roots of a quadratic equation. If you don't know it, look it up.
 
  • #10
ok, so when i take the derivative, i just factor it out
 
  • #11
hage567
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ok, so when i take the derivative, i just factor it out
What?? I don't understand what you mean by that.
 
  • #12
well ive learned about quadratic equations but i forgot what it was called,
well when i factored it out, i got 3(x^2+2x-8) then i factored it out

3(x+2)(x-4) ok thats easy, i forgot about that algebra stuff and trig and geo, like my calculus teacher said, it's not the calculus its all that old stuff that will get ya
 
  • #13
i mean 3 (x-2) (x+4)
 
  • #14
hage567
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i mean 3 (x-2) (x+4)
OK that's better I was just going to point that mistake out.
 
  • #15
yea hey thanks for reminding me about that,
 
  • #16
hage567
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No problem. But I would recommend looking up the quadratic formula and remembering it. It works for those times when factoring isn't obvious.
 

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