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Math Help - [SOLVED] Descartes's Rule Of Signs

  1. #1
    Member >_<SHY_GUY>_<'s Avatar
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    Thumbs down [SOLVED] Descartes's Rule Of Signs

    When Doing The Problems... determining and positive or negative real zeros i always get them wrong...

    I Just Dont Get It...

    Ex.

    f(x)= 2x^4-x^3+6x^2-x+5

    how is it 4 or 2 or 0 positive real zeros?
    None Negatives?
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  2. #2
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    Descartes' Sign Rule -- from Wolfram MathWorld

    Can you state Descartes's Rule Of Signs ?
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    Quote Originally Posted by Plato View Post
    Descartes' Sign Rule -- from Wolfram MathWorld

    Can you state Descartes's Rule Of Signs ?
    I Can... But Somehow I dont Know How... The Numbers Of Zeros End Up One Less Than The actual zeros...
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    Quote Originally Posted by Plato View Post
    Can you state Descartes's Rule Of Signs ?
    so in other words yu start counting changes from, lets say from my example: 5?

    but why would there be 4 or 2 or 0 positive zeros?
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    Quote Originally Posted by >_<SHY_GUY>_< View Post
    but why would there be 4 or 2 or 0 positive zeros?
    Well there are four changes in sign.
    So there are 4, 4-2=2, or 4-4=0 positive roots.
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    Smile



    Oh... now i get it!

    these texts books are not good at explaining... they use some other method.... it confuses the whole class. and the teacher goes sometimes by the book... thanks!
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