<=> ( 8x2 - 2x ) . ( 64x2 - 16x + 1 ) = 9
=> 512x4 - 128x3 +8x2 -128x3 + 32x2 - 2x = 9
=> 512x4 -256x3 + 40x2 - 2x - 9 = 0
=> ( 512x4 - 256x3 ) + ( 40x2 - 20x ) + ( 18x - 9 ) = 0
=> 256x3 . ( 2x - 1 ) + 20x . ( 2x -1 ) + 9. ( 2x - 1 ) = 0
=> ( 2x - 1 ) . ( 256x3 + 20x + 9 ) = 0 => ( 2x - 1 ) . ( 256x3 + 64x2 - 64x2 - 16x + 36x + 9 ) = 0
=> ( 2x - 1 ) . [( 256x3 + 64x2 ) - ( 64x2 + 16 ) + ( 36x + 9 )] = 0
=> ( 2x - 1 ) . [64x2 (4x + 1 ) - 16x (4x + 1 ) + 9 (4x + 1 ) ] = 0 => (2x - 1 ) . (4x + 1 ) . ( 64x2 - 16x + 9 ) = 0
=> 2x - 1 = 0 hoặc 4x + 1 = 0 hoặc 64x2 - 16x + 9 = 0
Vì 64x2 - 16x + 9 = (8x - 1 )2 + 8 > 0 nên 64x2 - 16x + 9 = 0 vô nghiệm
Vậy x = 1/2 hoặc -1/4
