Odpowiedź:
x⁴ - 11x² + 18 = 0
wprowadzam : t = x² ∧ t > 0
(x²)² - 11x² + 18 = 0 ∧ x² =t
t² - 11t + 18 = 0
Δ = (-11)² -4×1×18
Δ = 121 -72
Δ = 49
√Δ = 7
t₁ =(11-7)/2 = 2
∨ ∧ t > 0
t₂ = (11+7)/2 = 9
↓
(t₁ = 2 ∨ t₂ = 9 ) ∧ t = x²
↓
x² = 2 ∨ x² = 9
↓
x = √2 ∨ x = -√2 ∨ x = 3 ∨ x = -3
