They are ellipses...centre of 1,3....major axis of 2 and minor axis of 4
for z =0
u should get something like...
z^2 - 4 = (x-1)^2 + (y-3)^2/4
from this ...u need to put into the form of ellipse
1 = (x-h)^2 / a^2 + (y-k)^2/b^2
where a is the major axis, b the minor axis and (h,k) the...