Derive the equation of the parabola with a focus at (−5, −5) and a directrix of y = 7.

f(x) = −one twenty fourth(x − 1)2 − 5
f(x) = one twenty fourth(x − 1)2 − 5
f(x) = −one twenty fourth(x + 5)2 + 1
f(x) = one twenty fourth(x + 5)2 + 1

Respuesta :

Answer:

[tex]y = - \frac{1}{24} (x + 5) + 1[/tex]

Explanation

The directrix y=7, is above the y-value of the focus. The parabola must will open downwards.

Such parabola has equation of the form,

[tex] {(x - h)}^{2} = - 4p(y - k)[/tex]

where (h,k) is the vertex.

The vertex is the midway from the focus to the directrix

The x-value of the vertex is x=-5 because it is on a vertical line that goes through (-5,-5).

The y-value of the vertex is

[tex]y = \frac{ 7 + - 5}{2} [/tex]

[tex]y = \frac{ 2}{2} = 1[/tex]

The equation of the parabola now becomes

[tex]{(x + 5)}^{2} = - 4p(y - 1)[/tex]

p is the distance from the focus to the vertex which is p=|7-1|=6

Substitute the value of p to get:

[tex]{(x + 5)}^{2} = - 4 \times 6(y - 1)[/tex]

[tex]{(x + 5)}^{2} = - 24(y - 1)[/tex]

We solve for y to get:

[tex]y = - \frac{1}{24} (x + 5) + 1[/tex]

Answer:

f(x) = −one twentyfourth (x + 5)2 + 1

Step-by-step explanation: