x^2-2x-4xy+4y^2+4y
=(x²-4xy+4y²)-(2x-4y)
=(x-2y)²-2(x-2y)
=(x-2y-2)(x-2y)
1-mn(1-mn)-m^3 n^3
=1-(mn)³-mn(1-mn)
=(1-mn)(1+mn+m²n²)-mn(1-mn)
=(1-mn)(1+mn+m²n²-mn)
=(1-mn)(1+m²n²)