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-   -   Finding y-intercept of parabola, given vertex and point (https://www.askmehelpdesk.com/showthread.php?t=407254)

  • Oct 18, 2009, 08:31 AM
    alibeatles
    Finding y-intercept of parabola, given vertex and point
    I can't remember how to tackle this type of question, I don't need the answer, just the steps.

    Find the y-intercept of the parabola with a vertex of (-5,2) that passes through (-4,5)
  • Oct 18, 2009, 10:32 AM
    Unknown008

    Well, I don't know how you would do it, but I would have used the completed square formula to solve this.

    The completed square form of a general quadratic is [math]y = a(x + \frac{b}{2a})^2 - \frac{b^2}{4a} + c[\math]

    The vertex is given by

    That means, and

    Then, using your given point, you have another equation;

    You should be able to solve for a, b and c, then, set x to zero in your equation to have the y intercept.

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