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Point of Inflection Problem

  1. Apr 25, 2009 #1
    1. The problem statement, all variables and given/known data
    If the graph of y=x^3+ax^2+bx-8 has a point of inflection at (2,0), what is the value of b?
    the answer is 8.

    2. Relevant equations



    3. The attempt at a solution
    y'=3x^2+2ax+b
    y''=6x+2a
    Let y''=0=6x+2a then i plugged in 2 for x
    and got -6=a
    So y'=3x^2-12x+b...
    I dont know where to go from here.
     
  2. jcsd
  3. Apr 25, 2009 #2

    dx

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    Gold Member

    You get one more equation from the fact that y = 0 at x = 2.
     
  4. Apr 25, 2009 #3
    i wouldnt of thought of that.
    thank you
     
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