(x-2y)^2-4(2x+y)(y-2x)+4x(y-2)
=x^2-4xy+4y^2-4(y^2-4x^2)+4xy-8x
=x^2-4xy+4y^2-4y^2+16x^2+4xy-8x
=17x^2-8x
=x(17x-8)