请教绘图问题

[cfchenchen]

这是画的图:
x=linspace(-0.5,110,100);
y1 =(3*x.^2+1)./(x.^3+x+3);
y2 =6*x./(x.^3+x+3)-(3*x.^2+1).^2./(x.^3+x+3).^2;
subplot(2,2,1);plot(x,y1);title('一阶微分图形');
subplot(2,2,2);plot(x,y2);title('二阶微分图形');
subplot(2,2,3);plot(x,y1,x,y2);title('一阶与二阶微分混合图形');