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y34r23r0
y34r23r0 asked in Education & ReferenceHomework Help · 10 years ago

How can I find the equation of the quadratic function described?

If the graph is a parabola with vertex (3,-8) and passing through the origin.

1 Answer

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  • Justo
    Lv 7
    10 years ago
    Favorite Answer

    Let y = ax ^ 2 + bx + c.

    As passing through the origin,

    0 = a • 0 ^ 2 + b • 0 + c,

    c = 0

    As through (3, 8)

    8 = a • 3 ^ 2 + b • 3

    9a + 3b = 8

    But the abscissa of the vertex is -b/2a. That is, -b/2a = 3, b =-6a

    therefore

    9a + 3b = 9a – 18a = 8

    9a =- 8, a =- 8 / 9

    b =-6a = 48 / 9

    And the equation is

    y = -8 / 9 x ^ 2 + 48 / 9 x

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