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Math Help - I need this answer checked

  1. #1
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    I need this answer checked

    Need to find the roots of the polynomial equation

    x^3-5x^2+7x-35 = 0

    I got:

    f(1)=-32
    f(-1)=-48
    f(1/5)=-33
    f(-1/5)=-36
    f(1/7)=-34
    f(-1/7)=-36
    f(1/35)=-34
    f(-1/35)=-35

    I didn't bother rounding decimals but, I got no rational roots.. so If someone could verify this answer? Since my book does not have an answer key...
    Last edited by lax600; July 27th 2008 at 01:25 PM.
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  2. #2
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    Factor this equation first. Then find the roots.

    -Andy
    Attached Thumbnails Attached Thumbnails I need this answer checked-eqn1659.png  
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  3. #3
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    er... is it alowed to factor like that?
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  4. #4
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    When factoring x^3-5x^2+7x-35, first try to locate a GCF. In this case, your GCF is 1, so we move on. Try grouping the terms since we have 4 of them. (x^3 - 5x^2) + (7x - 35). We take the GCF of each group: [x^2 (x - 5)] and [7(x - 5)]. Nice, each group has the factor (x-5). Therefore, we can write our original equation as (x-5)(x^2 + 7). Expand (foil) this and check it for yourself!

    Any questions, don't hesitate to ask!
    -Andy
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  5. #5
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    well then... how would you factor 4x^3+16x^2-22x-10? I can't get it
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  6. #6
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    You have a GCF of 2 here. Start by factoring that out. Like this:

    2(2x^3 + 8x^2 - 11x - 5)

    -Andy
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