Find the focus and directrix of the following parabola:

[tex]\[ (x-5)^2 = 8(y-1) \][/tex]

Focus: [tex]\((5, ?)\)[/tex]
Directrix: [tex]\(y = \square\)[/tex]



Answer :

To find the focus and directrix of the parabola given by the equation [tex]\((x-5)^2 = 8(y-1)\)[/tex], follow these steps:

1. Identify the standard form:
The standard form of a parabola with a vertical axis is [tex]\((x-h)^2 = 4p(y-k)\)[/tex], where [tex]\((h, k)\)[/tex] represents the vertex of the parabola.

2. Extract the vertex:
Compare the given equation [tex]\((x-5)^2 = 8(y-1)\)[/tex] to the standard form [tex]\((x-h)^2 = 4p(y-k)\)[/tex]. Here, [tex]\(h\)[/tex] is 5 and [tex]\(k\)[/tex] is 1. Therefore, the vertex of the parabola is [tex]\((5, 1)\)[/tex].

3. Find the value of [tex]\(p\)[/tex]:
By comparing [tex]\((x-5)^2 = 8(y-1)\)[/tex] with [tex]\((x-h)^2 = 4p(y-k)\)[/tex], we can identify that [tex]\(4p\)[/tex] = 8. Solving for [tex]\(p\)[/tex], we get:
[tex]\[ 4p = 8 \implies p = 2 \][/tex]

4. Determine the focus:
The focus of the parabola with a vertical axis can be found using the coordinates [tex]\((h, k + p)\)[/tex]. Since [tex]\(h = 5\)[/tex], [tex]\(k = 1\)[/tex], and [tex]\(p = 2\)[/tex]:
[tex]\[ \text{Focus} = (5, 1 + 2) = (5, 3) \][/tex]

5. Determine the directrix:
The equation of the directrix for a parabola with a vertical axis is given by [tex]\(y = k - p\)[/tex]. Substituting [tex]\(k = 1\)[/tex] and [tex]\(p = 2\)[/tex]:
[tex]\[ \text{Directrix} = y = 1 - 2 = -1 \][/tex]

Thus, the focus and directrix of the given parabola [tex]\((x-5)^2 = 8(y-1)\)[/tex] are:

Focus: [tex]\((5, 3)\)[/tex]

Directrix: [tex]\(y = -1\)[/tex]

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