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mathcalculus

  • 2 years ago

mathcalculus HELP: Determine the values of where the tangent line is horizontal for the function:

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  1. mathcalculus
    • 2 years ago
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  2. mathcalculus
    • 2 years ago
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    i know i have to find the derivative and set it to zero but it's not coming out to be correct. can anyone help me

  3. mathcalculus
    • 2 years ago
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    so i did 3x^2-6x-4=0

  4. mathcalculus
    • 2 years ago
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    i tried to use the quadratic formula and got sqrt(21)+3/3

  5. mathcalculus
    • 2 years ago
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    + or - sqrt(21)+3/3

  6. mathcalculus
    • 2 years ago
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    also aka 2.52753...

  7. dumbcow
    • 2 years ago
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    derivative seems correct

  8. mathcalculus
    • 2 years ago
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    to find what x = to... ?

  9. mathcalculus
    • 2 years ago
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    i used quadratic formula

  10. mathcalculus
    • 2 years ago
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    @dumbcow dont i have to do that to find x??

  11. mathcalculus
    • 2 years ago
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    im getting it wrong,

  12. dumbcow
    • 2 years ago
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    yes everything looks correct to me...do they want exact or decimal answer?

  13. dumbcow
    • 2 years ago
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    http://www.wolframalpha.com/input/?i=3x%5E2-6x-4%3D0

  14. mathcalculus
    • 2 years ago
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    can i use quadratic formula for ths one?

  15. mathcalculus
    • 2 years ago
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    @dumbcow

  16. mathcalculus
    • 2 years ago
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    ??

  17. mathcalculus
    • 2 years ago
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    ????????????????????????

  18. dumbcow
    • 2 years ago
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    yes of course you use quadratic formula...thats how you got your answer that i said looked correct

  19. mathcalculus
    • 2 years ago
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    im not getting that using quadratic formula

  20. mathcalculus
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    im getting something totally different and wrong

  21. dumbcow
    • 2 years ago
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    \[x = \frac{3 \pm \sqrt{21}}{3}\]

  22. mathcalculus
    • 2 years ago
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    yes! but from 6+2*sqrt(21)/6?

  23. mathcalculus
    • 2 years ago
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    shouldnt it be 1+ or - sqrt 21/3

  24. dumbcow
    • 2 years ago
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    same thing, just a matter of splitting up fraction or keeping it as single fraction

  25. mathcalculus
    • 2 years ago
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    no it's not because the answer is 1+ sqrt (7/3) gives me 2.52753 and 1+sqrt 21/3 gives me 1.86086!

  26. mathcalculus
    • 2 years ago
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    @dumbcow

  27. dumbcow
    • 2 years ago
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    hmm \[\frac{\sqrt{7}}{\sqrt{3}} = \frac{\sqrt{21}}{3} \]

  28. mathcalculus
    • 2 years ago
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    hmmm?

  29. mathcalculus
    • 2 years ago
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    @dumbcow

  30. mathcalculus
    • 2 years ago
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    try it on a calculator.

  31. dumbcow
    • 2 years ago
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    http://www.wolframalpha.com/input/?i=1%2Bsqrt%287%2F3%29+%2C+1%2Bsqrt%2821%29%2F3

  32. dumbcow
    • 2 years ago
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    oh you added the "1" before dividing by "3"

  33. mathcalculus
    • 2 years ago
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    okay from my answer.... not the internet.. 6+2 sort(21)/3.... where do i go from there?

  34. dumbcow
    • 2 years ago
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    well it should be a 6 on bottom

  35. mathcalculus
    • 2 years ago
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    no i didn't add anything.

  36. mathcalculus
    • 2 years ago
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    okay sure a 6. i thought it could be a 3 to narrow it down

  37. mathcalculus
    • 2 years ago
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    so 6+or-2sqrt(21)/6

  38. dumbcow
    • 2 years ago
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    i dont see the problem, you posted answer in beginning... " i tried to use the quadratic formula and got sqrt(21)+3/3 "

  39. mathcalculus
    • 2 years ago
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    so it is a 3 in the denominator!

  40. dumbcow
    • 2 years ago
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    \[\frac{6 \pm 2\sqrt{21}}{6} = \frac{2(3 \pm \sqrt{21})}{6} = \frac{3 \pm \sqrt{21}}{3}\]

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