I am studying for a test and one of the review questions is stumping me.

I am suppose to find the center and radius of a circle with the following equation:

x^2 + 4x + y^2 - 6y + z^2 + 12z = 0

I know that the equation for a sphere is x^2 + y^2 + z^2 = radius ^2

Also I think that you would take (x - x at center)^2 + (y- y at center)^2 + (z -- z at center)^2 and this is equal to the radius squared. But I do not know how to deal with 4x, -6y and 12z.

Thanks to all you math enlightened folks for all the help that I have received for the past year!