a) Find the real values of x for which

(x^3)-4(x^2)-x+4>=0, which I got to be x>=4 and -1<=x<=1. That's right, right?

It's the next part that I'm really stuck with

b) Find the three lines in the (x,y) plane on which

(x^3)-4(x^2)y-x(y^2)+4(y^3)=0.

I'll be really grateful for your help.