Verified answer

[tex] \cos(390) = \cos(360 + 30) = \\ \\ \\ \cos(30) = \frac{ \sqrt{3} }{2} .[/tex]

Ответ:

√3/2

Объяснение:

cos(360° · n + a) = cos(a), n ∈ ℤ

cos(390°) =

= cos(360° + 30°) =

= cos(30°) = √3/2