(х+у)³ - (х-у)³-2у=(х+у-х+у)((х+у)²+(х+у)(х-у)+(х-у)²)-2у=
=(2у)(х²+2ху+у²+х²-у²+х²-2ху+у²)-2у=2у(х²+у²)
(a-b)³-(c+d)³-a+b+c+d=(a-b-c-d)((a-b)²+(a-b)(c+d)+(c+d)²)-(a-b-c-d)=
=(a-b-c-d)(a²-2ab+b²+ac-bc+ad-bd-1)=
x³-27+(x+3)²-3x=(x-3)(x²+3x+9)+x²+6x+9-3x=(x-3)(x²+3x+9)+(x²+3x+9)=
=(x²+3x+9)(x-3+1)=(x²+3x+9)(x-2)