Question

What is the radius of a circle whose equation is x2 + y2 – 10x + 6y + 18 = 0? how many units?

Answer 1

$(x-a)^2+(y-b)^2=r^2$
$x^2 + y^2 - 10x + 6y + 18 = 0\\\\ x^2-10x+y^2+6y+18=0 \\\\ (x-5)^2-25+(y+3)^2-9+18=0\\\\ (x-5)^2+(y+3)^2=16\\\\ r^2=16$
$r = \sqrt{16} \\\\ r=4$ 

Answer 2

(X^2.5x+25)+(y^2.3y+9)+18-25-9=0
(X-5)^2+(y+3)^21=16
Radius is 4