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Maths Conic Sections General Numeric Response
Published on: August 14, 2026

If 'r' be the radius of largest circle with centre (3, 0) that can be inscribed in the ellipse
9x 2 + 25y 2 = 225, then r is equal to

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The correct answer is:
21

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Sol. Largest circle will be that circle which touches the ellipse at any point (5cos θ θ , 3sin θ θ )

⇒ ⇒ Line joining points (5cos θ θ , 3sin θ θ ) and (3, 0) will be perpendicular to tangent of ellipse at point
(5cos θ θ , 3sin θ θ )

so that

or and

so that point on ellipse is .

Hence radius of circle is .

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