Question

Решите уравнение 10 cos^2 x- 19cos x + 7=0

Answer 1

10cos²x - 19cosx + 7 = 0

D = 361 - 280 = 81

cosx₁ = (19 + 9)/20 = 1,4 > 1 - не подходит

cosx₂ = (19 - 9)/20 = 0,5

x = +-π/3 + 2πk, k∈Z