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Homework Help: Screwy Equation?

  1. Jun 7, 2006 #1
    hey, I was given this function to analyze, and when it came to the x-intercepts i think i must be getting confused. The equation is (30x^4+23x^3-29x^2+6x)/x which i made into 30x^3+23x^2-29x+6x to make it easier to work with.

    Anyways i used newton's method and let my first value =0 to approximate a root and came out with 1/3. However when i used graphmatica, the curve does not pass through this point at all, but -1.5. THe wierd thing is that both these points, when subbed into the equation equal zero. Where am I messing this up? thanx
    Last edited: Jun 7, 2006
  2. jcsd
  3. Jun 7, 2006 #2
    6x / x is not 6x. Also, you may not want to make your first guess for newton's method lie on a discontinuity in the graph. Thirdly, according to descartes rule of signs that function should have over 1 real root. You probably botched plugging it into the program.
    Last edited by a moderator: Jun 7, 2006
  4. Jun 7, 2006 #3


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    When you divided by x you left a factor of x in the 6x term. It should just be x.

    However, you do have the right roots (-3/2, 1/3 and I'll leave the third to you!) so I suspect you entered the equation into Graphmatica incorrectly.
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