
182.
ա) cos(2π/7) + cos(4π/7) + cos(6π/7) = –1/2
բ) cos(π/5) + cos(3π/5) = 1/2
գ) sin(3π/10) – sin(π/10) = 1/2
183.
ա) 8cos10°·cos20°·cos40° = ctg10°
բ) 16cos20°·cos40°·cos60°·cos80° = 1
184.
ա) √(1 + sinx) + √(1 – sinx) = 2cos(x/2)
բ) √(1 + sinx) – √(1 – sinx) = 2sin(x/2)
185.
ա) (tg(α+β) – tgα – tgβ) / (tgα·tgβ·(tgα+tgβ)) = tgβ
բ) (tg(45°+α) – tg(45°–α)) / (tg(45°+α) + tg(45°–α)) = sin2α
186.
ա) (sinα + cosα) / cos³α = 1 + tgα + tg²α + tg³α
բ) (tg2α – 2tgα)(ctgα – tgα) = 2tg²α