ПОМОГИТЕ РЕШИТЬ!!!!!!!

Question

ПОМОГИТЕ РЕШИТЬ!!!!!!!

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Answer 1

Task/25238469
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4(Cos²π/8 -Sin²π/8) - 6Sin(π/4) =4*Cos(2*π/8) -6Sin(π/4) =
4*Cos(π/4) -6Cos(π/4) = -2Cos(π/4) = -2*(√2)/2 = - √2 . 

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Cos²φ -Sin²φ = Cos2φ  ; Sin(π/4) =Cos(π/4) = (√2)/2 .   π/4 =45°.

Answer 2

По формуле косинуса удвоенного аргумента:
cos²A - sin²A = cos2a, получаем:
4cos(π/4) - 6sin(π/4) = 4·√2/2 - 6·√2/2 = 2√2 - 3√2 = -√2