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Math Help - finding roots of cubic functions

  1. #1
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    finding roots of cubic functions

    my prof had a cubic function r^3 -4r^2 + 3r -1

    & quickly wrote down the roots: (r-1)^2(r-2)

    how did he do that so quickly? (he didn't write down the steps)
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by amyu2005 View Post
    my prof had a cubic function r^3 -4r^2 + 3r -1

    & quickly wrote down the roots: (r-1)^2(r-2)

    how did he do that so quickly? (he didn't write down the steps)
    um, that's not right. maybe when you get the right function we can show you the trick. there are several tricks that go with cubics. not all are done in the same way
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  3. #3
    Behold, the power of SARDINES!
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    Quote Originally Posted by amyu2005 View Post
    my prof had a cubic function r^3 -4r^2 + 3r -1

    & quickly wrote down the roots: (r-1)^2(r-2)

    how did he do that so quickly? (he didn't write down the steps)
    ummmmm...... I don't think that is correct.

    According to the rational roots theorem the only the only zero would be  \pm 1 but neither of these are zero's.

    This does not have any zero's over the rational numbers.

    Is there a typo?
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