Answer:
x² + y² = 81
Step-by-step explanation:
Standard form for the equation of a circle: (x - h)² + (y - k)² = r²
(where (h, k) is the center and r is the radius)
Given:
- radius (r) = 9
- center of circle = (0, 0)
⇒ (x - 0)² + (y - 0)² = 9²
⇒ x² + y² = 81
