Question

An equation of a circle is x^2 - 8x + 16 +y^2 + 10y + 25 = 81

Answer 1

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)