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mathcalculus Group Title

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

  • one year ago
  • one year ago

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  1. mathcalculus Group Title
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    • one year ago
  2. mathcalculus Group Title
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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

    • one year ago
  3. mathcalculus Group Title
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    so i did 3x^2-6x-4=0

    • one year ago
  4. mathcalculus Group Title
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    i tried to use the quadratic formula and got sqrt(21)+3/3

    • one year ago
  5. mathcalculus Group Title
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    + or - sqrt(21)+3/3

    • one year ago
  6. mathcalculus Group Title
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    also aka 2.52753...

    • one year ago
  7. dumbcow Group Title
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    derivative seems correct

    • one year ago
  8. mathcalculus Group Title
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    to find what x = to... ?

    • one year ago
  9. mathcalculus Group Title
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    i used quadratic formula

    • one year ago
  10. mathcalculus Group Title
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    @dumbcow dont i have to do that to find x??

    • one year ago
  11. mathcalculus Group Title
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    im getting it wrong,

    • one year ago
  12. dumbcow Group Title
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    yes everything looks correct to me...do they want exact or decimal answer?

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

    • one year ago
  14. mathcalculus Group Title
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    can i use quadratic formula for ths one?

    • one year ago
  15. mathcalculus Group Title
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    @dumbcow

    • one year ago
  16. mathcalculus Group Title
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    ??

    • one year ago
  17. mathcalculus Group Title
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    ????????????????????????

    • one year ago
  18. dumbcow Group Title
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    yes of course you use quadratic formula...thats how you got your answer that i said looked correct

    • one year ago
  19. mathcalculus Group Title
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    im not getting that using quadratic formula

    • one year ago
  20. mathcalculus Group Title
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    im getting something totally different and wrong

    • one year ago
  21. dumbcow Group Title
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    \[x = \frac{3 \pm \sqrt{21}}{3}\]

    • one year ago
  22. mathcalculus Group Title
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    yes! but from 6+2*sqrt(21)/6?

    • one year ago
  23. mathcalculus Group Title
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    shouldnt it be 1+ or - sqrt 21/3

    • one year ago
  24. dumbcow Group Title
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    same thing, just a matter of splitting up fraction or keeping it as single fraction

    • one year ago
  25. mathcalculus Group Title
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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!

    • one year ago
  26. mathcalculus Group Title
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    @dumbcow

    • one year ago
  27. dumbcow Group Title
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    hmm \[\frac{\sqrt{7}}{\sqrt{3}} = \frac{\sqrt{21}}{3} \]

    • one year ago
  28. mathcalculus Group Title
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    hmmm?

    • one year ago
  29. mathcalculus Group Title
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    @dumbcow

    • one year ago
  30. mathcalculus Group Title
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    try it on a calculator.

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

    • one year ago
  32. dumbcow Group Title
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    oh you added the "1" before dividing by "3"

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

    • one year ago
  34. dumbcow Group Title
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    well it should be a 6 on bottom

    • one year ago
  35. mathcalculus Group Title
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    no i didn't add anything.

    • one year ago
  36. mathcalculus Group Title
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    okay sure a 6. i thought it could be a 3 to narrow it down

    • one year ago
  37. mathcalculus Group Title
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    so 6+or-2sqrt(21)/6

    • one year ago
  38. dumbcow Group Title
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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 "

    • one year ago
  39. mathcalculus Group Title
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    so it is a 3 in the denominator!

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

    • one year ago
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