... (0,75đ) a 3 + 2c = (x + y) 3 + 2(x 3 + y 3 ) = 3x 3 + 3y 3 + 3x2y +3xy2 (0, 25) 3ab = 3( x + y)(x2 + y2) = 3x 3 + 3y 3 + 3x2y +3xy2 (0, 25) Vậy: a 3 + 2c = 3ab (0, 25) b/ (1,25đ) ... 5x 3 + 4x = x(x4 -5x2 + 4) (0, 25) = x[x2( x2-1)-4(x2-1)] (0 ,5) = x( x2-1)(x2-4) (0, 25) = (x-2)(x-1)x(x+1)(x+2) (0 ,5) b/ (1đ) A = a2(2a - 3) + b2( -3 + 2b) = 2(a 3 +b 3 ) -3( a2+b2) ... (1,25đ) x 3 - 3x + a = (x2 - 2x +1)(x +2) + a - 2(0, 75) (x 3 - 3x + a) chia hết cho (x - 1)2 ⇔a-2 = 0 ⇔a = 2 (0 ,5) b) (1,25đ) x2 (x -1) + 2x (1-x) = 0 ⇔x(x-1)(x-2) = 0 (0 ,5) Vậy x∈{0;1;2}...