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Homework Help: Maxima and Minima Problem

  1. Jan 11, 2005 #1
    Hello all

    Given [tex] y = -x^4 + 18x^2 + 11 [/tex] how would you find the intervals where the function is increasing and decreasing? Would you have to find [tex] f'(x) [/tex] and find critical points?

  2. jcsd
  3. Jan 11, 2005 #2


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    Yep, that's the most straightforward and surefire way to do it.
  4. Jan 11, 2005 #3
    yes that is the way to go...

    make a sign chart of the first derivative and you'll have all the info you need

  5. Jan 11, 2005 #4


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    Due to the biquadratic character of the function,the resulting 3-rd order equation (when setting the first derivative to zero) can be solved easily.
    One of the solutions is zero and is a local minimum.

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