【上岸】評論
(A)( 9x2-1 ) ( 3x+1 )=27x3+9x2-1-3x(B)( 9x2+1 ) ( 3x-1 )=27x3-9x2-1+3x(C)( 3x2-1 ) ( 9x+1 )=27x3+3x2-1-9x(D)( 3x2+1 ) ( 9x-1 )=27x3-3x2-1+9x