What is the equation of a parabola whose vertex is (0, 5) and whose directrix is x = 2?

A.
y2 = 8(x − 5)

B.
8(y − 5) = x2

C.
(y − 5)2 = 8x

D.
(y − 5)2 = -8x

Respuesta :

ANSWER

C.

[tex]{(y - 5)}^{2} = 8x [/tex]

EXPLANATION

It was given that, the vertex of the parabola is (0,5).

The directrix of this parabola is x=2.

The directrix tells us that, the parabola will open horizontally in the positive x-axis direction.

Hence the equation of this parabola is of the form;

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

we plug in the vertex h=0, k=5 to get,

[tex]{(y - 5)}^{2} = 4p(x - 0)[/tex]

p is the distance from the vertex to the directrix, which is

[tex]p = 2 - 0 = 2[/tex]

Hence, we the equation of the parabola becomes,

[tex]{(y - 5)}^{2} = 4 \times 2(x - 0)[/tex]

[tex]{(y - 5)}^{2} = 8x [/tex]

Answer: D.  (y − 5)2 = -8x

Step-by-step explanation: I got this correct on Edmentum.

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