What is the critical number of the function f(x)= x^3 + 3x^2-24x?

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SUMMARY

The critical number of the function f(x) = x³ + 3x² - 24x is determined by finding where its derivative, f'(x) = 3x² + 6x - 24, equals zero. The derivative simplifies to 3(x + 2)(x - 4), yielding critical points at x = -2 and x = 4. Understanding the quadratic nature of the derivative is essential for solving for critical numbers. Familiarity with factoring and the quadratic formula is crucial for accurately identifying these points.

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afcwestwarrior
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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
 
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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.
 
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
 
afcwestwarrior said:
so i just plug in any numbers in the x's

Eeh??
Do you know what an equation is, and how to solve it??
 
i think ido, can u show me an example
 
yes i know what an equation is, but how do i solve it
 
Can you name what type of equation that is?
 
well I am on the section maximum and minum values, it doesn't say what kind of equation it is, id say its a critical number equation
 
well I am on the section maximum and minum values, it doesn't 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
afcwestwarrior said:
ok, so when i take the derivative, i just factor it out

What?? I don't understand what you mean by that.
 
  • #12
well I've 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 that's 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
afcwestwarrior said:
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
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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