10-2. Parabola, Ellipse, Hyperbola
hard

If the radius of the largest circle with centre $(2,0)$ inscribed in the ellipse $x^2+4 y^2=36$ is $r$, then $12 r^2$ is equal to

A

$72$

B

$115$

C

$92$

D

$69$

(JEE MAIN-2023)

Solution

$(x-2)^2+y^2=r^2$

Solving with ellipse, we get

$(x-2)^2+\frac{36-x^2}{4}=r^2$

$3 x^2-16 x+52-4 r^2=0$

$D=0 \Rightarrow 4 r^2=\frac{92}{3}$

Standard 11
Mathematics

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