Tìm x, biết:

a) (x + 4)(x² – 4x + 16) – x(x – 5)(x + 5) = 264;

b) (x – 2)³ – (x – 2)(x²² + 2x + 4) + 6(x – 2)(x + 2) = 60.

a) (x + 4)(x² – 4x + 16) – x(x – 5)(x + 5) = 264

⇔ (x + 4)(x² – 4x + 4²) – x(x² – 5²) = 264

⇔ x³ + 4³ – x³ + 25x = 264

⇔ 25x = 200

⇔ x = 8.

b) (x – 2)³ – (x – 2)(x²² + 2x + 4) + 6(x – 2)(x + 2) = 60

⇔ x³ – 6x² + 12x – 8 – (x³ – 2³) + 6(x² – 4) = 60

⇔ x³ – 6x² + 12x – 8 – x³ + 8 + 6x² – 24 = 60

⇔ 12x = 84

⇔ x = 7.