function Fplot
    
    x0 = 1/4;
    y0 = 1/8;
    z = -5:0.01:5;
    plot (z, 0*z, 'k', z, -8*z.^3 + 12*z.^2 + 27.*(y0-x0));
    axis([-2,2,-2,2])


end

