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Homework Help: How to get Formula from a Cubic Graph

  1. Jan 12, 2010 #1
    1. The problem statement, all variables and given/known data

    The figure shows the graph of a cubic polynomial.


    The function graphed is f(x)=

    Hint: You may write the function as f(x) = a(x-b)(x-c)(x-d) where b, c, and d, are integers and a is a fraction.

    2. Relevant equations

    3. The attempt at a solution

    I'm lost...
  2. jcsd
  3. Jan 12, 2010 #2


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    When f(x)=0 the graph cuts the x-axis, so what are the values of b,c and d?
  4. Jan 12, 2010 #3


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    b, c and d are where f(x)=0, can't you read those off from the graph? Now what about a?
  5. Jan 12, 2010 #4
    I'm sorry but both of those answers made no sense...
  6. Jan 12, 2010 #5


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    Homework Helper

    Are you unable to read the number off of the graph? Which part made no sense?
  7. Jan 13, 2010 #6


    Staff: Mentor

    Simply by observing the graph you should be able to find b, c, and d in your equation f(x) = a(x -b)(x - c)(x - d).

    And you should be able to get a by noticing where the graph crosses the y-axis.
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