What is the equation of a circle whose center is at the origin and whose radius is 9? x^2  + y^2  = 3x^2  + y^2  = 9x^2  + y^2  = 81

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!

Sis less than or equal to 75 (bottom left)