text: In order to graph a circle you have to solve the equation for y.  Using the generic equation for a circle:\n\n(x-h)^2 + (y-k)^2 = r^2\n(y-k)^2 = r^2 - (x-h)^2\ny-k= + or - sqrt(r^2 - (x-h)^2)\ny= + or - sqrt(r^2 - (x-h)^2) + k\n\nSo plug in\n\ny1 = sqrt(r^2 - (x-h)^2) + k\ny2 = -sqrt(r^2 - (x-h)^2) + k\n\nYou have to have both in order to have the top and bottom of the circle.\n\nNote: h and k are the coordinates of the center of the circle.  The center is (h, k), so if you want a circle centered at the origin, h and k are both 0.