text: ti-84 to graph a circle? i can't get my calculator (ti-84) to graph circles only lines.. can anyone help?? in order to graph a circle you have to solve the equation for y.  using the generic equation for a circle:  (x-h)^2 + (y-k)^2 = r^2 (y-k)^2 = r^2 - (x-h)^2 y-k= + or - sqrt(r^2 - (x-h)^2) y= + or - sqrt(r^2 - (x-h)^2) + k  so plug in  y1 = sqrt(r^2 - (x-h)^2) + k y2 = -sqrt(r^2 - (x-h)^2) + k  you have to have both in order to have the top and bottom of the circle.  note: 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.