189 (2,4,6) Решите, пожалуйста

2) x⁴ - 20x² + 64 = 0
x² = t
t² - 20t + 64 = 0
D = 400 - 256 = 144
√D = 12
t₁ = (20-12)/2 = 4
t₂ = (20+12)/2 = 16

x² = 4
x² = 16

x = +-2
x = +-4

Ответ: -4; -2; 2; 4

4) x⁴ - 20x² + 100 = 0
x² = t
t² - 20t + 100 = 0
(t - 10)² = 0
t = 10

x² = 10
x = +-√10

Ответ: -√10; √10

6) x⁴ - 8x² + 15 = 0
x² = t
t² - 8t + 15 = 0
D = 64 - 60 = 4
√D = 2
t₁ = (8-2)/2 = 3
t₂ = (8+2)/2 = 5

x² = 3
x² = 5

x = +-√3
x = +-√5

Ответ: -√5; -√3; √3; √5