Tính: a) (x^2 - 6)(x^2 + 6); b) (x - 1)(x^2 + x + 1).

a) (x² - 6)(x² + 6) = x² . x² + x² . 6 - 6 . x² - 6 . 6

= x⁴ - 36.

b) (x - 1)(x² + x + 1) = x . x² + x . x + x . 1 - 1 . x² - 1 . x - 1 . 1

= x³ + x² + x - x² - x - 1

= x³ + (x² - x²) + (x - x) - 1

= x³ - 1