Ответ(ы) на вопрос:
Гость cos2π/5 ·cos2π/3 ·cosπ·cos4π/3·cos5π/3 =
= cos72 ·cos(π-π/3) ·(-1)·cos(π+π/3)·cos(2π-π/3)=
= - cos72· (-cosπ/3)·(-cosπ/3)·cosπ/3 = -1/8· cos72 =
= -1/8 ·[(√5-1)/4] = (1-√5)/32
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