To do this problems you need to know how to use the technique of completing the square so you can put this in the form of (x-h)^2 + (y-k)^2 = r^2 when (h,k) are the coordinates of the vertex. If you dont know how to complete the square you should look this up ( there are many fine videos on line)
x^2 +16x +y^2 -36 =0
x^2 +16x + (y-0)^2 =36 to convert x^2 +16 x take half the coefficient of the x term to give you (x-8)^2. in doing this you now have this in the form of (x-h)^2 but you have also added (8)^2 or 64 to the left side of the equation so all you need to do is subtract 64 to keep things balanced
So now you have (x-8)^2 -64 + (y-0)^2 = 36
(x-8)^2 + (y-0)^2 = 36 +64=100
So the center is at (8,0) and the radius id sq root of 100= 10
