c2 Differentiation

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  1. Ganhad's Avatar
    1 14-04-2012  02:55
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    c2 Differentiation
    y=3(x-4)/2x^3
    y=x^3(3x+8/x) diff these i carry on getting the wrong answer
  2. raheem94's Avatar
    2 14-04-2012  03:07
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    Re: c2 Differentiation
    (Original post by Ganhad)
    y=3(x-4)/2x^3
    y=x^3(3x+8/x) diff these i carry on getting the wrong answer
    What answer do you get?

    For the first one,
    \displaystyle y=\frac{3(x-4)}{2x^3}=\frac{3x-12}{2x^3}=\frac{3x}{2x^3}-\frac{12}{2x^3}=\frac{3}{2x^2}-\frac{6}{x^3}=\frac32x^{-2}-6x^{-3}

    Now differentiate it.

    For the second one,
    \displaystyle y=x^3\left(3x+\frac8{x}\right)=3 x^4 + 8x^2
    Differentiate it.
    Last edited by raheem94; 14-04-2012 at 03:11.
  3. raheem94's Avatar
    3 14-04-2012  03:09
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    Re: c2 Differentiation
    (Original post by TheStudentBoom)
    first one:

    y= 3x-12/ 2x^3
    y = 3x/2x^3 - 12/2x^3

    y = 3/2x^2 - 6/x^3 => y= (3/2 x^-2) - (6x^-3)
    dy/dx = -3x^-3 + 12x^-4

    therefore dy/dx = -3/x^3 + 12/x^4

    might have done something wrong there, but thats what I know. I'll do the second one in a seperate post.
    Your answer is wrong.

    By the way, please don't post full solutions. Full solutions are considered a last resort.
  4. TheStudentBoom's Avatar
    4 14-04-2012  03:09
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    Re: c2 Differentiation
    (Original post by raheem94)
    What answer do you get?

    For the first one,
    \displaystyle y=\frac{3(x-4)}{2x^3}=\frac{3x-12}{2x^3}=\frac{3x}{2x^3}-\frac{12}{2x^3}=\frac{3}{2x^2}-\frac{6}{x^3}=\frac32x^2-6x^{-3}
    hey the last bit is 3/2 x^-2 - 6x^-3 right? not 3/2 x^2?
  5. TheStudentBoom's Avatar
    5 14-04-2012  03:10
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    Re: c2 Differentiation
    (Original post by raheem94)
    Your answer is wrong.

    By the way, please don't post full solutions. Full solutions are considered a last resort.
    Very sorry, I'll just delete my posts then.
    Post rating:
    1
  6. raheem94's Avatar
    6 14-04-2012  03:11
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    Re: c2 Differentiation
    (Original post by TheStudentBoom)
    hey the last bit is 3/2 x^-2 - 6x^-3 right? not 3/2 x^2?
    Thanks for indicating my mistake. I will edit my post.
  7. raheem94's Avatar
    7 14-04-2012  03:13
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    Re: c2 Differentiation
    (Original post by TheStudentBoom)
    Very sorry, I'll just delete my posts then.
    +rep to you
  8. Ganhad's Avatar
    8 14-04-2012  05:28
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    Re: c2 Differentiation
    (Original post by raheem94)
    +rep to you
    book says something different i did get what you got -_- Damn Book could you show me this one aswell y=3sqrtx(x-2)^2
  9. raheem94's Avatar
    9 14-04-2012  05:31
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    Re: c2 Differentiation
    (Original post by Ganhad)
    book says something different i did get what you got -_- Damn Book could you show me this one aswell y=3sqrtx(x-2)^2
    What is the answer in the book for the previous question?
  10. raheem94's Avatar
    10 14-04-2012  05:32
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    Re: c2 Differentiation
    (Original post by Ganhad)
    book says something different i did get what you got -_- Damn Book could you show me this one aswell y=3sqrtx(x-2)^2
    Is this your new question \displaystyle y=3\sqrt{x(x-2)^2}
  11. Ganhad's Avatar
    11 14-04-2012  05:48
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    Re: c2 Differentiation
    no the root does not go over the bracket just over the x

    (Original post by raheem94)
    Is this your new question \displaystyle y=3\sqrt{x(x-2)^2}
    Last edited by Ganhad; 14-04-2012 at 05:54.
  12. raheem94's Avatar
    12 14-04-2012  06:05
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    Re: c2 Differentiation
    (Original post by Ganhad)
    no the root does not go over the bracket just over the x
    \displaystyle y=3\sqrt{x}(x-2)^2 = 3x^{\frac12}(x^2-4x+4)=3x^{\frac52}-12x^{\frac32}+12x^{\frac12}

    Now its simple to differentiate it.

    By the way, what is the answer of the previous question in the book?
  13. Ganhad's Avatar
    13 14-04-2012  06:09
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    Re: c2 Differentiation
    im supposed to find the gradient of that curve where x = 3 the answer is supposed to be 29root3 could you check if you get that please
  14. Ganhad's Avatar
    14 14-04-2012  06:15
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    Re: c2 Differentiation
    (Original post by raheem94)
    \displaystyle y=3\sqrt{x}(x-2)^2 = 3x^{\frac12}(x^2-4x+4)=3x^{\frac52}-12x^{\frac32}+12x^{\frac12}

    Now its simple to differentiate it.

    By the way, what is the answer of the previous question in the book?
    -3x^-3+6x^-4
  15. raheem94's Avatar
    15 14-04-2012  06:19
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    Re: c2 Differentiation
    (Original post by Ganhad)
    im supposed to find the gradient of that curve where x = 3 the answer is supposed to be 29root3 could you check if you get that please
    Which question is it?

    You have posted 3 questions in this thread, which is this?
  16. raheem94's Avatar
    16 14-04-2012  06:22
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    Re: c2 Differentiation
    (Original post by Ganhad)
    -3x^-3+6x^-4
    Is this the answer to \displaystyle y=\frac{3(x-4)}{2x^3}=\frac{3x-12}{2x^3}=\frac{3x}{2x^3}-\frac{12}{2x^3}=\frac{3}{2x^2}-\frac{6}{x^3}=\frac32x^{-2}-6x^{-3} \ ?

    If this is the case then it is wrong, the correct answer should be \displaystyle -3x^{-3}+18x^{-4}
  17. Ganhad's Avatar
    17 14-04-2012  06:30
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    Re: c2 Differentiation
    i agree but could you see if u get 29 root 3 if you sub x=3 into \displaystyle y=3\sqrt{x}(x-2)^2 = 3x^{\frac12}(x^2-4x+4)=3x^{\frac52}-12x^{\frac32}+12x^{\frac12}
  18. raheem94's Avatar
    18 14-04-2012  06:36
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    Re: c2 Differentiation
    (Original post by Ganhad)
    i agree but could you see if u get 29 root 3 if you sub x=3 into \displaystyle y=3\sqrt{x}(x-2)^2 = 3x^{\frac12}(x^2-4x+4)=3x^{\frac52}-12x^{\frac32}+12x^{\frac12}
    Substituting x=3 in \displaystyle y=3\sqrt{x}(x-2)^2 give 3\sqrt3

    Substituting x=3 in the derivative of \displaystyle y=3\sqrt{x}(x-2)^2 gives \displaystyle \frac{13\sqrt3}2
  19. Ganhad's Avatar
    19 14-04-2012  06:40
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    Re: c2 Differentiation
    this book is wak -_- so many damn mistakes
  20. Ganhad's Avatar
    20 14-04-2012  15:53
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    Re: c2 Differentiation
    (Original post by raheem94)
    Substituting x=3 in \displaystyle y=3\sqrt{x}(x-2)^2 give 3\sqrt3

    Substituting x=3 in the derivative of \displaystyle y=3\sqrt{x}(x-2)^2 gives \displaystyle \frac{13\sqrt3}2
    the equation of a curve is y= x^2-5x-24/x

    find the gradient of the curve at each of the point were the curve crosses the x-axis how would you do this sorry for asking for so much help but im a thicko that has been doing this for neardy 1 1/2 days straight
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