Answer:
the radius: r = 9
the center: (4, -5)
Step-by-step explanation:
The equation of a circle:
(x - a)² + (y - b)² = r²
(a, b) - the center of a circle
r - the radius of a circle
x² - 8x + 16 + y² + 10y + 25 = 81
(x² - 2(x)(4) + 4²) + (y² + 2(y)(5) + 5²) = 81
use: (a - b)² = a² - 2ab + b² and (a + b)² = a² - 2ab + b²
(x - 4)² + (y + 5)² = 9²
Therefore
the radius: r = 9
the center: (4, -5)
