x . ( x + 4 ) . ( x + 6 ) . ( x + 10 ) + 128
= ( x2 + 10x ) . ( x2 + 10x + 24 ) + 128
đặt x2 + 10x + 12 = y, đa thức đã cho có dạng :
( y - 12 ) . ( y + 12 ) + 128 = y2 - 16 = ( y - 4 ) . ( y + 4 )
= ( x2 + 10x + 16 ) . ( x2 + 10x + 8 ) = ( x + 2 ) . ( x + 8 ) . ( x2 + 10x + 8 )