4（2y-x）+25（x-2y）³
=4（2y-x）-25（2y-x）³
=（2y-x）[4-25（2y-x）²]
=（2y-x）[4+5（2y-x）][4-5（2y-x）]
=（2y-x）（4+10y-5x）（4-10y+5x）．