IIT-JEE 1995 ScreeningQuestion 1
The radius of the circle passing through the foci of the ellipse $\dfrac{x^{2}}{16}+\dfrac{y^{2}}{9}=1$, and having its centre at $(0,3)$ is
Ellipse
Solution
Foci $(\pm\sqrt{16-9},0)=(\pm\sqrt7,0)$. Radius$^2=7+3^2=16$, so $r=4$.