Q. A focus of an ellipse is at the origin. The directrix is the line $x = 4$ and the eccentricity is $\frac{1}{2,}$ then length of semi major axis is
A) 5/3
B) 8/3
C) 2/3
D) 4/3
Explanation
(b)
Since, $\frac{a}{e} - ae = 4\$and $e = \frac{1}{2}$
$\therefore\ 2a - \frac{a}{2} = 4\$
$\Rightarrow \ a = \frac{8}{3}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.