Tìm x biết

tìm x biết 
a) x ( x2 - 1 ) + x2 ( 3 - x ) = 0
b) ( x - 1 ) ( x2 + x + 1 ) + 9 = 0 
c) 3x ( 12x - 4 ) - 9x ( 4x - 3 ) = 30
d ) ( 12x - 5 ) ( 4x - 1 ) - ( 3x - 7 ) ( 1 + 16x ) = 81