lg²(x-1) - 2*lg(x-1)=15
одз x > 1
lg(x - 1) = y
y² - 2y - 15 = 0
D = b² - 4ac = 4 + 60 = 64
y₁₂ = (2 +- 8)/2 = 5 -3
y₁ = -3
lg(x₁ - 1) = -3
x₁ - 1 = 10^(-3)
x₁ = 1.001
y₂ = 5
lg(x₂ - 1) = 5
x₂ - 1 = 10^5
x₂ = 100001
