Question

What is the radius of the circle given by the equation below?

Answer 1

$x^2+18x+y^2+18y=-146 \\ \\( x^2+18x + 81)+(y^2+18y+81)-81-81=-146\\ \\(x+9)^2+(y+9)^2=-146+81+81\\ \\(x+9)^2+(y+9)^2=-146+162\\ \\(x+9)^2+(y+9)^2=16$
 
$This \ is \ in \ the \ general \ circle \ form : (x-h)^ 2+ (y-k)^2 = r^2, so: \\ \\ r^2=16 \\ \\r=\sqrt{16}\\ \\r=4 \\ \\ Answer : \ C. 4$