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How to find the equation of a parabola.

  1. Apr 22, 2007 #1
    1. The problem statement, all variables and given/known data
    Find the equation of the parabola if you have the following information:
    Xintersects: (-4;0) and (0;0)
    Yint: y = 7
    Vertex: (-2;7)



    2. Relevant equations
    The equation must be in the standard form:
    y=ax^2 + bx + c


    3. The attempt at a solution
    I know how to put it into the equation y = a(x^2 - p) + q but I have no idea how to put it into the y=ax^2 + bx + c form, which is asked.


    Thanks
     
  2. jcsd
  3. Apr 22, 2007 #2

    cristo

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    I think you mean you know how to put it in the form y = a(x - p)2 + q. Why not put it in this form and then expand the right hand side so it looks like y=ax2+bx+c?
     
  4. Apr 22, 2007 #3
    Alright but unfortunately I have got no idea how to do that. Could you please elaborate?
     
  5. Apr 22, 2007 #4

    cristo

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    Expand the right hand side to give y=a(x2-2px+p2)+q. Now can you spot the value of a,b and c in y=ax2+bx+c from this above expression?
     
  6. Apr 22, 2007 #5
    Oh my word I cant believe I did not see that before!

    Thank you! :rofl:
     
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