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anonymous

  • one year ago

What is the equation of a parabola with a vertex at (1, -1) and a directrix y = 4.

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  1. anonymous
    • one year ago
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    @muscrat123

  2. muscrat123
    • one year ago
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    yes

  3. muscrat123
    • one year ago
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    and i do not know this

  4. anonymous
    • one year ago
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    >.>

  5. freckles
    • one year ago
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    hello.

  6. freckles
    • one year ago
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    \[(x-h)^2=4p(y-k) \\ \text{ where the vertex is } (h,k) \]

  7. freckles
    • one year ago
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    p's sign is based on whether the vertex is above the directrix or below the directrix if the vertex is above the directrix, then p is positive. if the vertex is below the directrix, then p is negative.

  8. freckles
    • one year ago
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    now the other thing p has going for it .. is that it is the distance from the vertex to the directrix (or you can say the distance from the vertex to the focus)

  9. freckles
    • one year ago
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    so p tells us two things not just one

  10. freckles
    • one year ago
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    it helps to draw what we are given sometimes... |dw:1439673047228:dw| so the directrix is above the vertex so p is negative can you tell me how far the directrix is from the vertex

  11. anonymous
    • one year ago
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    thx so much, i think the answer is \[y+1= -\frac{ 1 }{ 20 }\left( x-1 \right)^{2}\]

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