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12th grade Math?

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How would you factor 3x^3-4x^2+4x-1?
P.S. Factor theorem does not work here.

  • 12th grade Math? - ,

    Look for the first root by trial and error. Using the "q/p theorem", I see that one solution is +1/3. So, (x - 1/3) is one factor.
    Divide that into 3x^3-4x^2+4x-1 to get a quadratic factor,
    (3x^2 -3x +3) = 3 (x^2 -x +1).
    The term in parentheses can be factored by the usual means, but gives two complex roots.
    3x^3-4x^2+4x-1 = 3(x- 1/3)(x^2-x+1)
    (3x-1)(x^2-x+1))

  • 12th grade Math? - ,

    What's the q/p theorem though?

  • 12th grade Math? - ,

    I was afraid you'd ask me that :-)
    The more common name for it is the rational roots test (or theorem).

    Here is a reference.

    http://en.wikipedia.org/wiki/Rational_root_theorem

    It doesn't always provide a root, but if there is a rational real root, it works.

    Briefly, it says that if the constant term of the polynomial is q and the first term in p, and if there are rational real roots, one of the roots will be
    +/- q/p or +/- the tio of prime-number factors of q and p.

  • eapmo dzywoakr - ,

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