(x-2y)分之4y^2+(4y^2-x^2)分之4x^2y+x+2y
=4y²(x-2y)/(x²-4y²)-4x²y/(x²-4y²)+x+2y
=(4xy²-8y³-4x²y)/(x²-4y²)+x+2y
=(-8y³+x³-4xy²+2x²y-8y³)/(x²-4y²)
=(x³-4xy²+2x²y-16y³)/(x²-4y²)