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Finding equations w/ two given points:

  1. Oct 12, 2006 #1
    Ok there are two give points and I need to find the equation:

    Points: (-3,0), (-.5,0)

    My work:

    y=(x+3)(x+.5)
    y=x^2+.5x+3x+15

    Completed the square:

    -15= x^2+3.5x
    -15=x^2+3.5x+3.0625
    -11.9375=(x+1.75)^2
    y= (x+1.75)^2+11.9375

    What did I do wrong??
     
  2. jcsd
  3. Oct 12, 2006 #2
    [tex] y = (x+3)(x+.5) = x^{2}+3.5x + 1.5[/tex]

    you multiplied 3 by 5, instead of 3 by 0.5
     
  4. Oct 12, 2006 #3
    ohhh lol thanks.
     
  5. Oct 12, 2006 #4

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Why did you assume a quadratic function? Two points determine a straight line. The constant function y= 0 passes through (-3, 0), (-5, 0).
    In fact there are an infinite number of functions whose graph pass through those two points.
     
  6. Oct 12, 2006 #5
    Halls, he meant the zeros of the function. He is doing quadratic equations after all.
     
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