a) $ x ( x - 4 ) ( x + 4 ) - ( x - 3 )^{3} - 6x + 2 $
$ = x ( x^{2} - 16 ) - ( x^{3} - 3 . x^{2} . 3 + 3 . x . 3^{2} - 3^{3} ) - 6x + 2 $
$ = x^{3} - 16x - x^{3} + 9x^{2} - 27x + 27 - 6x + 2 $
$ = 9x^{2} - 49x + 29 $
b) $ x ( 3 + 2x ) ( 3 - 2x ) + 4x ( x + 1 )^{2} - 2x^{2} -12 $
$ = x ( 9 - 4x^{2} ) + 4x ( x^{2} + 2x + 1 ) - 2x^{2} - 12$
$ = 9x - 4x^{3} + 4x^{3} + 8x^{2} + 4x - 2x^{2} - 12 $
$ = 6x^{2} + 13x - 12 $
CHÚC HỌC TỐT !!!