What is the equation of the quadratic graph with a focus of (8, −8) and a directrix of y = −6?

A) f(x) = −one fourth (x − 7)2 + 1
B) f(x) = −one fourth (x − 8)2
C) f(x) = −one fourth (x − 8)2 − 7
D) f(x) = one fourth (x − 7)2

Respuesta :

Answer:

[tex]y=-\frac{223}{28}(x-8)^2-7[/tex]

Step-by-step explanation:

we are given a quadratic equation

we know that quadratic equation is same as equation of parabola

so, we can use formula

[tex]y=a(x-h)^2+k[/tex]

Focus is

[tex](h,k+\frac{1}{4a} )[/tex]

now, we can compare it with given focus

=(8,-8)

we get

[tex]h=8[/tex]

[tex]k+\frac{1}{4a}=-8[/tex]

Directrix is

[tex]y=k-\frac{1}{4a}[/tex]

we are given directrix =-6

[tex]k-\frac{1}{4a}=-6[/tex]

we got two equations as

[tex]k+\frac{1}{4a}=-8[/tex]

[tex]k-\frac{1}{4a}=-6[/tex]

now, we can add both equations

and we get

[tex]k+\frac{1}{4a}+k-\frac{1}{4a}=-8-6[/tex]

[tex]2k=-8-6[/tex]

[tex]2k=-14[/tex]

[tex]k=-7[/tex]

now, we can find 'a'

[tex]k+\frac{1}{4\times -7}=-8[/tex]

[tex]k=-\frac{223}{28}[/tex]

now, we can plug back all values

and we get

So, equation of parabola is

[tex]y=-\frac{223}{28}(x-8)^2-7[/tex]


Answer:

The answer is C