=[(x+2y)(x-2y)+4y²]/(x-2y)-4x²y/ (x+2y)(x-2y)=x²/(x-2y)-4x²y/(x+2y)(x-2y)=(x³+2x²y-4x²y)/(x+2y)(x-2y)=x²/(x+2y)(4y²-x²)=-(x+2y)(x-2y)