3 cos2x - 14 cosx + 7 = 0 Решите уравнение. Created by termun. matematika-ru

3 cos2x - 14 cosx + 7 = 0 Решите уравнение...

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3 cos2x - 14 cosx + 7 = 0 Решите уравнение

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3(2cos²x - 1) - 14cosx + 7 = 0
6cos²x - 3 - 14cosx + 7 = 0
6cos²x - 14cosx + 4 = 0
3cos²x - 7cosx + 2 = 0
D = 49 - 24 = 25
cosx = (7+5)/2 = 2 >1 - не подходит
cosx = (7-5)/6 = 1/3
x = +-arccos(1/3) + 2πk, k∈Z

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