Решение
5) (x - 6√x + 8)/(4 - √x) = - (x - 6√x + 8)*(√x - 4)
x - 6√x + 8 = 0
√x = t
t² - 6t + 8 = 0
t₁ = 2
t₂ = 4
√x = 2
√x = 4
x - 6√x + 8 = (√x - 2)*(√x - 4)
- (√x - 2)*(√x - 4) / (√x - 4)] = 2 - √x
7) x⁴ - 8x² - 9 = 0
x² = t, t > 0
t² - 8t - 9 = 0
t₁ = - 1, не удовлетворяет условию t > 0
t₂ = 9
x² = 9
x₁ = - 3
x₂ = 3
Ответ: x₁ = - 3 ; x₂ = 3
10) y = √(x² + 5x)
x² + 5x ≥ 0
x(x + 5) ≥ 0
x = 0; x = - 5
x ∈ (- ∞; - 5]∪[0; + ∞)