Question

What is the equation of the directrix for the following parabola: (x - 1)2 = 12(y + 2) A. y = -5 B. X = -5 C. y = -3 D. y = -12

Answer 1

The general equation of parabola with vertex (h,k) is,

`(x-h)^2=4p(y-k)`

The quation of directrix for the given parabola is,

`y=k-p`

On comparing the given equation with general equation,

h = 1, k = -2 and 4p = 12.

Determine the value of p.

`\begin{gathered} 4p=12 \\ p=3 \end{gathered}`

Determine the equation of directric for given parabola.

`\begin{gathered} y=-2-3 \\ y=-5 \end{gathered}`

So answer is y = -5.

Option A is correct.