a)
x ( x + 4 ) ( x + 6 ) ( x + 10 ) + 128
= ( x^ 2 + 10 x ) ( x ^2 + 10 x + 24 ) + 128
= ( x ^2 + 10 x + 12 − 12 ) ( x ^2 + 10 x + 12 + 12 ) + 128
= ( x ^2 + 10 x + 12 ) − 12^ 2 + 128
= ( x^ 2 + 10 x + 12 ) 2 − 16
= ( x^ 2 + 10 x + 12 − 16 ) ( x 2 + 10 x + 12 + 16 )
= ( x ^2 + 10 − 4 ) ( x 2 + 10 x + 28 )