Question

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

Answer 1

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