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Differentiation of sec^3( )

  1. Jan 2, 2015 #1
    1. The problem statement, all variables and given/known data
    i have to derive this equation
    ## sec^3(x^3+csc^-1(cot^3\frac{x+4}{3x})) ##

    2. The attempt at a solution

    ## 3sectan^2(x^3+csc^-1(cot^3\frac{x+4}{3x}))*(3x^2-\frac{1}{|cot^3\frac{x+4}{3x}|\sqrt(cot^6\frac{x+4}{3x}-1)})*(-3csc^2\frac{x+4}{3x})*(\frac{3x*1-(x+4)(3)}{9x^2})##

    is it so far right?
  2. jcsd
  3. Jan 2, 2015 #2


    Staff: Mentor

    First off, it's not an equation. Second, you are differentiating the expression, not deriving it. Starting with the equation ax2 + bx + c = 0, I can derive the quadratic formula, and this has nothing to do with calculus differentiation.
    Doesn't look right to me. It should start off with 3sec2(<bunch of other stuff>).

    BTW, problems involving calculus should be posted in the Calculus section, not the Precalc section. I have moved this thread.
  4. Jan 2, 2015 #3


    User Avatar
    Gold Member

    Looks like you have a lot of chain rule to apply. first off make the substitution u = sec(junk inside), then du =? plugging it in ##\frac{d}{dx}f(u) = \frac{df}{du}\frac{du}{dx}## keep making substitutions until you get rid of all the composites. for example, after you make the intial substitution, you need to make another one, composed within u, say v = junk inside, then dv = ? then within v, you have another etc...
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