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Need help writing equation of parabola?

Write the equation in standard form of the parabola with vertex (7,5) and directrix = 1.

Update:

Oh sorry directrix x = 1.

5 Answers

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  • 8 years ago
    Favorite Answer

    Vertex (7, 5):

    h = 7

    k = 5

    Directrix:

    x = 1

    Since the directrix is to the left of the vertex, the parabola will be horizontally-oriented and opening to the right.

    p = h - x:

    p = 7 - 1

    p = 6

    a = 1 / 4p:

    a = 1 / 4(6)

    a = 1/24

    Equation:

    x = a(y - k)² + h:

    x = 1/24 (y - 5)² + 7

    x = 1/24 (y² - 10y + 25) + 7

    x = 1/24 y² - 5/12 y + 25/24 + 7

    x = 1/24 y² - 5/12 y + 25/24 + 168/24

    x = 1/24 y² - 5/12 y + 193/24

    ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

    or

    x = 0.0417y² - 0.4167y + 8.0417

    ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

     

    Source(s): 4/27/13
  • 8 years ago

    Standard equation:

    y= a(x-h)^2 + k {(h,k) is the vertex}

    Re-written as:

    (x – 7)^2 = 4p(y – 5) {4p = 1/a}

    Assuming Directrix Y=1,

    Distance between vertex and directrix = absolute value (1-5) = +4 = p

    (x-7)^2 = 4(4)(y-5)

    y-5 = [(x-6)^2]/16

    y= [(x-6)^2]/16 + 5

  • ?
    Lv 7
    8 years ago

    Directrix cannot = 1

    It can be x = 1 or y = 1

  • Anonymous
    5 years ago

    Y = x^2 - 6x - 1 ==> y = (x^2 - 6x + 9) - 1 - 9 ==> y = (x - 3)^2 - 10 EDIT: relying on the learn, the typical types of parabolas do differ. In this case, the reply is A. Hope this helps!

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  • 8 years ago

    (x-7)^2 +(y-5)^2 =(x-1)^2

    x^2-14x +49 +y^2-10y +25 =x^2-2x+1

    y^2-10y +25 =12x-48

    (y-5)^2 =12x-48

    12x =(y-5)^2+48

    x = (1/12)(y-5)^2 +4 ...............Ans

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