Question

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

Answer 1

Answer:

D.

Step-by-step explanation:

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

2) then

$d(focus)=\sqrt{(x-1)^2+(y+4)^2} \ and \ d(directrix)=|x-3|;$

$\sqrt{(x-1)^2+(y+4)^2} =|x-3|;$

3) after evoluation the equation:

(y+4)²=-4x+8 or (y+4)²= -4(x-2);

4) correct answer is D.