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Math Help - Rational Zero

  1. #1
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    Rational Zero

    list all possible rational zeros of f.

    f(x)=3x^4 + 4x^3 -5x^2 -8
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  2. #2
    Super Member Bacterius's Avatar
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    Do you know what a rational zero is ? It actually is a non-complex root of the equation. Let us solve f(x) = 0 :

    3x^4 + 4x^3 -5x^2 -8 = 0

    Can you solve it now ?
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  3. #3
    Grand Panjandrum
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    Quote Originally Posted by Bacterius View Post
    Do you know what a rational zero is ? It actually is a non-complex root of the equation. Let us solve f(x) = 0 :

    3x^4 + 4x^3 -5x^2 -8 = 0

    Can you solve it now ?
    WRONG!, that would make \sqrt{2} a rational zero of x^2-2

    A rational number is a number that can be written as the ratio of two integers.

    This question is meant to be addressed using the rational root theorem, which tells you that any rational root of a polynomial equation with integer coefficients is the ratio of a factor of the constant term to a factor of the coefficient of the highest power occuring.

    So for:

    3x^4 + 4x^3 -5x^2 -8 = 0

    the rational roots are amoung \pm1,\ \pm 2,\ \pm 4,\ \pm 8,\ \pm1/3,\ \pm 2/3,\ \pm 4/3,\ \pm 8/3

    You try each of these to find which are actual roots.

    CB
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  4. #4
    Super Member Bacterius's Avatar
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    Aah

    Sorry sorry ! Here, a thanks to forgive me
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