Question

The focal distance of a point on the parabola $y^2=8x$ is $4$. Its ordinates are:

• A. $\pm 1$
• B. $\pm 2$
• C. $\pm 3$
• D. $\pm 4$

Answer 1

Answer: (D)

Given parabola is $y^2=8x$ and focal distance $=4$
Comparing this with standard parabola, $y^2=4ax$
$a=2$, co-ordinate of focus is $(2,0)$.
Focal distance of any point $(x,y)=x+2$

$\Rightarrow x+2=4$
$\Rightarrow x=2$
$y^2=8x=8\times 2=16$
$\Rightarrow y=\pm 4$