Hi there!
Points on circle are equidistant from its center.
This is th' distance called the radius of the circle.
• Cartesian form:-
r : √x² + y² = 9
r : x² + y² = 9²
r : x² + y² = 81
Hence,
Option 3ʳᵈ : x² + y² = 81 is Correct.
~ Hope it helps!
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