arcCos²x - 8arcCosx + 15 = 0
arcCosx = m , 0 ≤ m ≤ π
m² - 8m + 15 = 0
m₁ = 3 m₂ = 5
1) arcCosx = 3 3 ∈ [0 , π]
x = Cos3
2) arcCosx = 5 5 ∉ [0 ; π]
x = Cos5
ответ : Cos3
