Question

If the vertex of the parabola is at origin and its directrix is $x-3=0$, then the length of its latus rectum is

Answer 1

Since, the vertex of parabola is at origin and its directrix is $x-3=0$
The parabola will be of the form $y^2=-4ax$
The directrix will be $x=a$
$\Rightarrow x-3=0\Rightarrow x=3$
$\Rightarrow a=3$
Length of its latus rectum $=4a=12$