(tg(n/2-a)-ctg(n/2+a))2-(ctg(n+a)+ctg(3n/2+a))2 выражение

Tg(π/2 - α) = ctg α
ctg (π/2 + α) = - tg α
ctg (π + α) = ctg α
ctg (3π/2 + α) = - tg α
(ctg α + tg α)² - (ctg α - tg α)² =
= (ctg α + tg α + ctg α - tg α)(ctg α + tg α - ctg α + tg α) =
= 2ctgα · 2tgα = 4
ответ: 4