(х +1)(х - 1)(х - 2)(х - 4) = 7
((х + 1)(х - 4)((х - 1)(х - 2)) = 7
(х² - 4х + х - 4)(х² - 2х - х + 2) = 7
(х² - 3х - 4)(х² - 3х + 2) = 7
х² - 3х = у
(у - 4)(у + 2) = 7
у² + 2у - 4у - 8 - 7 = 0
у² - 2у - 15 = 0
D = (-2)² - 4 · 1 · (-15) = 4 + 60 = 64; √64 = 8
y₁ = (2 - 8)/2 = -3
y₂ = (2 + 8)/2 = 5
x² - 3x = -3
x² - 3x + 3 = 0
D = (-3)² - 4 · 1 · 3 = 9 - 12 = -3 < 0 - нет решений
x² - 3x = 5
x² - 3x - 5 = 0
D = (-3)² - 4 · 1 · (-5) = 9 + 20 = 29
x₁₂ = (3 +-√29)/2