Question: I can't get the answer by simplify and expand

I've the equation

(-x^2+eta^2+2*x*xi+2*x*eta-xi^2-2*xi*eta-2*x*y-2*y*eta+2*xi*y+y^2)*(-x^2-2*x*eta+eta^2+2*x*xi+2*xi*eta-xi^2+2*x*y-2*xi*y-2*y*eta+y^2)-(x-xi)^4+6*((x-xi)^2)(-y+eta)^2-(-y+eta)^4

The answer is 0

But I can't get the answer by simplify and expand

Then which .Thanks

Please Wait...