( x" + x + 1 )" - 6x" - 6x - 33
——看到( x" + x + 1 ),就应该想到立方差
= ( x" + x + 1 )" - 6x" - 6x - 6 - 27
= ( x" + x + 1 )" - 6( x" + x + 1 ) - 27
= ( x" + x + 1 )" - 9( x" + x + 1 ) + 3( x" + x + 1 ) - 27
= ( x" + x + 1 )( x" + x + 1 - 9 ) + 3( x" + x + 1 - 9 )
= ( x" + x + 1 - 9 )( x" + x + 1 + 3 )
= ( x" + x - 8 )( x" + x + 4 )