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Calc BC Exam Question

  1. Apr 13, 2008 #1
    I'm doing a calc BC practice exam and I found this question that stumps me to the max:

    The function y=x^4+bx^2+8x+1 has a horizontal tangent and a point of inflection for the same value of x. What must be the value of b?


    I know that points of inflection are found from the second derivative and setting that function to zero, however the 'b' value really throws me off :yuck:

    Oh btw here are the mc answers.

    a) -6 b)-1 c) 1 d) 4 e) 6
     
  2. jcsd
  3. Apr 13, 2008 #2

    lurflurf

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    under what conditions does the function have a hotizontal tangent
    Under what conditions does the function have a point of inflection
    once you know that it should be easy to see when both occur
    you will also see what b must be
     
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