What is the radius of a circle given by equation x^2 + y^2 - 2x + 8y - 47 = 0

X^2 + y^2 - 2x + 8y - 47 = 0

x^2 + y^2 - 2x + 8y = 47

(x^2 - 2x) + (y^2 + 8y) = 47

(x^2 - 2 (1) x) + (y^2 + 2 (4) y) = 47

(x^2 - 2 (1) x + 1^2) + (y^2 + 2 (4) y + 4^2) = 47 + 1^2 + 4^2

(x - 1) ^2 + (y + 4) ^2 = 64 = 8^2

r=8