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Establishing inflection point

  1. Jan 26, 2012 #1
    Hello, the following fraction is the derivative of a function:

    (160-40t^2) / (t^2+4)^2

    According to my textbook they have established the inflection points by equating the top line of this derived fraction to zero and then solving for x e.g. 160-40t^2 = 0. (t=+-2).

    I was wondering is it a rule that you can simply equate the top line of a fraction format derivative to zero or am I missing something particular to this equation ?

    Thanks for any clarification.
  2. jcsd
  3. Jan 26, 2012 #2


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    Hey fran1942.

    What is the structure of your function? Is your derivative in terms of dy/dt = your expression in t or is dt/dx = expression in t?
  4. Jan 26, 2012 #3


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    Inflection points are points where the second derivative is 0, not the first derivative. It is true that a fraction is equal to 0 if and only if the numerator is 0.
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