Question

What is the equation of the parabola, in vertex form, with focus at (1,-4) and
directrix x= 3?

Answer 1

D.

Explanation:

1) according to the definition of parabola d(focus)=f(directrix),

2) then

`d(focus)=√((x-1)^2+(y+4)^2) \ and \ d(directrix)=|x-3|;`

`√((x-1)^2+(y+4)^2) =|x-3|;`

3) after evoluation the equation:

(y+4)²=-4x+8 or (y+4)²= -4(x-2);

4) correct answer is D.