Question

If $(-3,0)$ is the vertex and y-axis is the directrix of a parabola, then its focus is at the point

• A. $(0,-6)$
• B. $(-6,0)$
• C. $(6,0)$
• D. $(0,0)$
• E. $(3,0)$

Answer 1

The correct option is B $(-6,0)$

Let the coordinates of focus is $(h,0)$
$\Rightarrow (\frac{h+0}{2},\frac{0+0}{2})=(-3,0)$
$\Rightarrow (\frac{h}{2},0)=(-3,0)$
$\Rightarrow h=-6$
Hence focus is $(-6,0)$