304.sagews

y=var('y')
s=var('s')
t=var('t')
r=var('r')
u=var('u')
v=var('v')
z=var('z')

plot3d(x^2/4 +y^2/4,(x,-10,10),(y,-10,10))

parametric_plot3d((cos(r)*cos(s), sin(r), cos(r)*sin(s)), (r,-3,3), (s,0,2*pi))