Q. The straight line $x + y = c\$will be tangent to the ellipse$\ \frac{x^{2}}{9} + \frac{y^{2}}{16} = 1,$ $c$ is equal to
A) 8
B) $\pm 5$
C) $\pm 10$
D) $\pm 6$
Explanation
(b)
Condition for tangency to the ellipse is
$c^{2} = a^{2}m^{2} \pm b^{2}$
$\Rightarrow \ c^{2} = 9( - 1)^{2} \pm 16$
$c^{2} = 25$
$\Rightarrow \ \ c = \pm 5$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.