Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Calculus Differentiation Question

  1. Aug 4, 2006 #1
    I am just learning calculus, and I have to differentiate a problem. I have worked on it and I have asked people, but they do not know. Here is what I have done thus far:

    f(x) = 3x-6 – 8x5 + 9x2/5 + √7
    f(x) = 3(dx-6/dx) – 8(dx5/dx) + 9(dx2/5/dx) + √7(d/dx)
    f(x) = 3(-6x5) – 8(5x4) + 9(2/5x-3/5) + 0
    f(x) = -18x5 – 40x4 + 18/5x-3/5

    I am wondering if this is it, or whether I need to do more? If I need to do more, could you say which rule I should use or some other type of advice?

    Thanks

    P.S. If it is wrong, could you please tell me as well.
     
  2. jcsd
  3. Aug 4, 2006 #2

    berkeman

    User Avatar

    Staff: Mentor

    Your notation is a bit confusing. What is the starting function f(x)? And are you asked to find d[f(x)]/dx? Are all the "x" in your equations the unknown "x", or are some of the multiplication symbols?
     
  4. Aug 4, 2006 #3
    if you mean that your function is

    [tex]f(x) = 3x^{-6} - 8x^5 + 9x^{\frac{2}{5}}+\sqrt{7}[/tex]

    and you found that the derivative is

    [tex]f^\prime (x) = -18x^5 - 40 x^4 + \frac{18}{5}x^{-\frac{3}{5}},[/tex]

    (I don't know why you've written f(x)= at every line when you are trying to differentiate)

    then you have made a small error, because

    [tex]\frac{d(x^{-6})}{dx} = -6x^{-7},[/tex]

    not [itex]-6x^5[/itex]. Other than that it's ok (if I have translated your rather cryptic notation correctly - try to learn LaTeX: https://www.physicsforums.com/showthread.php?t=8997)
     
    Last edited: Aug 4, 2006
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook