Найдите ctg B,если tg...

Tg(b + pi/3) = 2√3
tg(b + pi/3) = (tgb + tg(pi/3))/(1 - tgb*tg(pi/3)) = (tgb + √3) / (1 - √3*tgb) = 2√3
ctgb = 1/tgb
(tgb + √3) / (1 - √3*tgb) = 2√3
2√3*(1 - √3*tgb) = tgb + √3
2√3 - 6tgb = tgb + √3
7tgb = √3
tgb = √3/7
ctgb = 7/√3