function plot1
hold on
grid on
axis ([-10,10,-10,10])
[x0,y0]=ginput(1);

plot(x0,y0,'r.','MarkerFaceColor',[1,0,0])
x=-10:1/100:10;
if y0>0
    z=((x+3*y0^(1/3)-x0).^3)./27;
else 
    z=(x-3*(-y0)^(1/3)-x0).^3./27;
end
plot (x,z)



end

