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Ответ:

1

Пошаговое объяснение:

cos(2π - β) = cos(-β) = cosβ

sin(-3π/2 + β) = sin(-3π/2 + β + 2π) = sin(β + π/2) = cosβ

cos(β - 3π) = cos(β - 3π + 4π) = cos(β + π) = -cosβ