clf;
[X,Y] = meshgrid(-8:.1:8); 
Z = 9 - X.*X - Y.*Y;
surf(X,Y,Z)
colormap hsv
hold on
surf(X,Y,ones(size(Z)).*9, 'FaceColor','red','EdgeColor','none')
alpha(.4)
%camlight left; 
%lighting phong
plot3(0,0,9,'w:+')
k=-150:0.1:100;
plot3(zeros(size(k)),zeros(size(k)),k);
hold off