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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