[x,t]=meshgrid(0:.05:5,0:0.05:5);
R= 8*t.*x.^3 - 4*x.^4 - 108*t.^2 + 72*t.*x - 8*x.^2 - 4;
figure(1)
contour(x,t,R,[0 0],'linewidth',2)