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Math Help - Find quadratic function from given vertex and a point

  1. #1
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    Find quadratic function from given vertex and a point

    The vertex coordinates they provide are (-2, 5), and the point that the parabola passes through is (0, 9). First, I mentally imagined the points on a plane to determine whether "a" was positive or negative; then I took the coordinates from the vertex point, which represent (h, k), and sent up my problem. It came out to be y = (x + 1)^2 - 5, but in the answer key the 5 (which is k) was positive. Why is this so?
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  2. #2
    MHF Contributor Siron's Avatar
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    Re: Find quadratic function from given vertex and a point

    You know in general a quadratic function looks like:
    y=a(x-h)^2+k with the vertex (h,k) so in this case you know for sure the equation has to be:
    y=a(x+2)^2+5
    You only have to determine a which can be done by enter the given point where the parabola goes through.
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