Question

The length of the latus rectum of a parabola, whose vertex and focus are on the positive $x-$ axis at a distance $R$ and $S(>R)$ respectively from origin, is

• A. $2(S-R)$
• B. $4(S-R)$
• C. $2(S+R)$
• D. $4(S+R)$

Answer 1

The correct option is B $4(S-R)$

$OA=R$ and $OB=S$
Focal length,
$AB=a=S-R$
$\therefore$ Length of latus rectum $=4(S-R)$