Объяснение:
2sin²x - 3√2cosx - 4 = 0
2(1 - cos²x ) - 3√2cosx - 4 = 0
2 - 2cos²x - 3√2cosx - 4 = 0
-2cos²x - 3√2cosx - 2 = 0
2cos²x + 3√2cosx + 2 = 0
Замена: cosx = t, t ∈ [-1 ; 1]
2t² + 3√2t + 2 = 0
D = 18 - 16 = 2
t₁ = 
t₂ =
∉ [-1 ; 1]
cosx = 
x = ± 
На отрезке
x = 