Question

Line $L=0$ cuts the conic $S=0$ at $A$ and $B$ and the equation $S+\lambda L^2=0$ represent a circle for some $\lambda ={\lambda }_1$ (say), the circle $S+{\lambda }_1{L}^2=0$ will touch the conic $S=0$ at both $A$ and $B$. Also if $L=0$ is tangent to conic $S=0$ the circle $S+{\lambda }_1{L}^2=0$ has radius equal to radius of curvature of the conic at the point of contact.
Radius of curvature at the end point of major axis of ellipse $\frac{x^2}{a^2}+\frac{y^2}{b^2}=1(a>b)$ is equal to -

• A. Latus rectum
• B. Semi latus rectum
• C. Semi minor axis
• D. None of these

Answer 1

Answer: (B)

Correct answer is (b) Semi latus rectum