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Where did I go wrong?

  1. Feb 7, 2006 #1

    Find the derivative of the function: [​IMG]

    My answer:

    Can please someone tell me where I messed up.

    Edit: i used that chain rule or something like that

    So first I changed the equation into [5x+(3x+sqrt(2x))^.5]^.5

    then I found the first derivative, so it was .5[5x+(3x+sqrt(2x))^.5]^-.5

    Next I did it for 5x and the 1/2 power-> 5+.5(3x+sqrt(2x))^-.5

    I did the same for the following 2 steps. I hope that helps.
    Last edited: Feb 7, 2006
  2. jcsd
  3. Feb 7, 2006 #2


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    Gold Member

    If you can show us what you did step-by-step (i know, that's hard with square roots unfortunately), we can help you determine where you went wrong.
  4. Feb 7, 2006 #3


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    Science Advisor

    your brackets are messed up. The last (third) bracketed factor does not multiply everything, just the part that starts with 3x.
  5. Feb 7, 2006 #4
    which brackets?
  6. Feb 8, 2006 #5
    sorry to bump the topic

    but could someone please explain what bracket krab means.
  7. Feb 8, 2006 #6


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    Homework Helper

    It may be quite impossible for us to guess your approach, and thus, we don't know where you went wrong. Now, may I ask you to post step by step solution, so that we can check it for you. :)
    You don't have to LaTeX, or use MS Equation Editor, just jot down your steps in a paper, then use a scanner and post it here. :)
    You can also learn how to LaTeX. There are three PDFs on the first post of that thread. The thread is a sticky in the Math & Science Tutorials board.
  8. Feb 8, 2006 #7
    He means that the "inner derivatives" do not multiply the entire expression. The last bracket - which by the way is not correct - is not supposed to be multiplied with the entire expression. It has to be inside the second bracket.

    EDIT: Explained better hopefully, without giving out too much of the solution.
    Last edited: Feb 8, 2006
  9. Feb 8, 2006 #8


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    What is meant is that the grouping (where the parentheses are) is incorrect.

    [tex]\frac{d}{dx}\sqrt{3x+\sqrt{2x}} \neq \left(3+\frac{.5}{\sqrt{2x}}\right)*2[/tex]
  10. Feb 8, 2006 #9


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    The 3rd big bracketed factor has to be INSIDE the bracket just ahead of it. IOW, it does not multiply the 5+ of the second big bracketed factor.
  11. Feb 8, 2006 #10
    [tex] \frac{1}{2}(3x+(2x)^{1/2})^{1/2})^{-1/2}*(5+\frac{1}{2}(3x+(2x)^{1/2})^{-1/2}*(3+\frac{1}{2}(2x)^{-1/2}*2))[/tex]




    Last edited: Feb 8, 2006
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