Решите уравнение 6sin^2 x-cosx-5=0

Question

Решите уравнение
6sin^2 x-cosx-5=0

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Answer 1

6(1 - Cos²x) - Cosx - 5 = 0
6 - 6Cos²x - Cosx -5 = 0
6Cos²x + Cosx -1 = 0
D = 25
Cosx = (-1+5)/12= 1/3                      б) Cosx = (-1 -5)/12 = -1/2
x = +-arcCos1/3 + 2πk, k ∈Z                   x = +-2π/3+ 2πn, n ∈Z