1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Polynomial Functions (word problem)

  1. Sep 29, 2011 #1
    1. The problem statement, all variables and given/known data
    A quartic function has x-intercepts of -5, -1, 2, and 4. The point (3.-8) lies on the curve. Determine an equation of the function.

    2. Relevant equations

    3. The attempt at a solution
    y = k (x+5)(x+1)(x-2)(x-4)
    Expanded form: f(x)=kx^4 + 9x^2 - 38x + 40 <---My expanded form is most likely wrong because expanding a quartic function tends to get clustered and confusing.

    Other than this I have absolutely no idea how to solve this question.
  2. jcsd
  3. Sep 29, 2011 #2


    User Avatar
    Homework Helper

    This looks fine.

    Unfortunately, your expansion is wrong. First show your steps, so we can see where the mistake is in your work.
  4. Sep 29, 2011 #3


    User Avatar
    Homework Helper

    I wouldn't even expand yet. I would find k first by plugging 3 and -8 for x and y into the factored form. Then I would multiply out the factors, and distribute the k value last.
  5. Sep 30, 2011 #4


    User Avatar
    Homework Helper

    Valid point. It's much easier to solve for k in this form.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Polynomial Functions (word problem)