(2x-y)(-y+2y)(y+x)(y²+4)
=(2x-y)(y)(y+x)(y²+4)
=y(2x-y)(x+y)(y²+4)
=y(2x²+xy-y²)(4+y²)
=y(8x²+4xy-4y²+2x²y²+xy^3-y^4)
=8x²y+4xy²-4y^3+2x²y^3+xy^4-y^5