var('s,t')
def x(t) :
return 10*cos(t)
def y(t) :
return 10*sin(t)
def z(x,y) :
return 4+(x^2-y^2)/100
S = parametric_plot3d([x(t),y(t), s*z(x(t),y(t))],(t,0,2*pi),(s,0,1), color= "darkgreen", opacity = 0.35)
C = parametric_plot3d([x(t),y(t), z(x(t),y(t))],(t,0,2*pi), color= "red", thickness= 2)
show(S+C, frame_aspect_ratio = [1,1,3])