Question

cos2x10cosx-11=0
срочно,помогите пожалуйста

Answer 1

Ответ:

cos2x-10cosx-11=0

2cos^2x-1-10cosx-11=0

2cos^2x-10cosx-12=0

cos^2x-5cosx-6=0

x2 - 5x - 6 = 0

D = b2 - 4ac

D = 25 + 24 = 49 = 7^2

x1,2 = -b ± √D/2a

x1 = 5 + 7/2 = 12/2= 6

x2 = 5 - 7/2 = - 2/2 = -1

 x1 = 6; x2 = -1

cosx=6 - (не удолт)

cosx=-1 -> x=pi+2pi*k , к-N

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