Show that the equation represents a sphere, and find its center and radius.
$ x^2 + y^2 + z^2 - 2x - 4y + 8z = 15 $
center $(1,2,-4), \quad r=6$
So the way that we're going to do this is by using completing the square. So ahh. Completing the square here. Not too difficult to see. Hey, um, get something that looks like that. And then well, we just to write this stuff out and then we got nine is twenty one single toe five. Right. This stuff out right here. So the center that one too negative for in the radius of six.