Question 372618
  <pre><font size = 3 color = "indigo"><b>
Hi,
The standard equation of a circle with center C(h,k) and radius r is :
{{{(x - h)^2 + (y - k)^2 = r^2}}}
Find the center and the radius  
x^2+y^2-8x+6y+9=0
completing the squares
x^2-8x +   y^2+6y         +9=0
(x-4)^2 + (y+3)^2 -16 -9 + 9 = 0
(x-4)^2 + (y+3)^2 = 16 = 4^2
radius = 4, center (4,-3)
{{{drawing(500,500, -2,10,-10,2,grid(1),circle(4,-3,4), circle(4,-3,.15), 
line(4,-3,0,-3),locate(4,-3,C),locate(2,-3,r))}}}