Question

Answer 1

a) x³ - 3x² + 3x - 1 = 1000

(x - 1)³ = 1000

(x - 1)³ = 10³

x - 1 = 10

x = 10 + 1

x = 11

b) x² - 4x - 21 = 0

x² + 3x - 7x - 21 = 0

(x² + 3x) - (7x + 21) = 0

x(x + 3) - 7(x + 3) = 0

(x + 3)(x - 7) = 0

x + 3 = 0 hoặc x - 7 = 0

*) x + 3 = 0

x = -3

*) x - 7 = 0

x = 7

Vậy x = -3; x = 7

c) 9x⁴ - 6x² - 3 = 0

9x⁵ - 9x² + 3x² - 3 = 0

(9x⁴ - 9x²) + (3x² - 3) = 0

9x²(x² - 1) + 3(x² - 1) = 0

(x² - 1)(9x² + 3) = 0

x² - 1 = 0

(x - 1)(x + 1) = 0

x - 1 = 0 hoặc x + 1 = 0

*) x - 1 = 0

x = 1

*) x + 1 = 0

x = -1

Vậy x = -1; x = 1