(-x/2-2y)(x/2-2y)
=-(x/2+2y)(x/2-2y)
=(2y+x/2)(2y-x/2)
=4y²-x²/4
(x²-3y)(3y-x²)
=-(x²-3y)(x²-3y)
=-x^4+6x²3y-3y²