Решение
Cos2x+3sin^2x=1,25
1 - 2sin²x + 3sin²x = 1,25
sin²x = 1 - 1,25
sin²x = 0,25
sin²x = 1/4
1) sinx = - 1/2
x = (-1)^n*arcsin(- 1/2) + πk, k ∈ Z
x = (-1)^(n+1)*arcsin(1/2) + πk, k ∈ Z
x = (-1)^(n+1)*(π/6) + πk, k ∈ Z
2) sinx = 1/2
x₁ = (-1)^n*arcsin(1/2) + πn, n ∈ Z
x₂ = (-1)^n*(π/6) + πn, n ∈ Z