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Homework Help: Help: derivative and critical #'s

  1. Oct 16, 2004 #1
    I can't seem to find the f ' (x) of the following:

    1) f(x) = -2x - ((128)/(x+9))

    2) f(x) = (x+4)^2 (x-10)^3
    (Find the number x at which the function f(x) = (x+4)^2 (x-10)^3 takes on an absolute minimum on the interval 4 < x < 10 (note: < means greater than or equal to )
  2. jcsd
  3. Oct 16, 2004 #2


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    1. It's just -2+128/(x+9)^2. Do you understand why?
    2. Do you know how to take the derivative of a product of two functions?
  4. Oct 16, 2004 #3


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    The derivative of -2x is -2. To differentiate ((128)/(x+9) use the quotient rule.

    To differentiate (x+4)^2 (x-10)^2 you will need to use the product rule.
    (and the chain rule but the derivatives of both x+4 and x- 10 are 1 so it doesn't really show up.)
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