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Нужно знать:

sin(-α) = -sinα, tg(-α) = -tgα, cos(-α) = cosα - из четности(нечетности)

sinπ = 0, tgπ = 0, cosπ = -1

α = -7π

sinα = sin(-7π) = -sin(7π) = -sin(6π + π) = -sinπ = 0

cosα = cos(-7π) = cos(7π) = cos(6π + π) = cosπ = -1

tgα = tg(-7π) = -tg(7π) = -tg(6π + π) = -tgπ = 0