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sonicfan12

  • 3 years ago

How do you do the Descartes rule of signs?

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  1. askme12345
    • 3 years ago
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    substitute all your x's for negative x :)

  2. sonicfan12
    • 3 years ago
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    Will you show me an example please?

  3. LagrangeSon678
    • 3 years ago
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    first count the sign changes in the original polynomial, the compute f(-x) and count the sign changes

  4. askme12345
    • 3 years ago
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    Sure - Lets say your equation is -5x^3 + 4x^2 - 5x So you have negative, positive, negative = this means 3 positive zeros (when youre solving for zeros) decartes rule says when you put -x into the equation you'll get your negative zeros .. here we go -5(-x)^3 + 4(-x)^2 -5(-x) (All even powers, will become negative, odds stay the same) 5x^3 - 4x2 + 5x .. so we have postive to negative to positive .. therefore 3 positive zeros

  5. satellite73
    • 3 years ago
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    purplemath has a good example and explanation

  6. satellite73
    • 3 years ago
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    http://www.purplemath.com/modules/drofsign.htm

  7. sonicfan12
    • 3 years ago
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    Thanx for the help! XD

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