Замена tg(x/4) = y, тогда ctg(x/4) = 1/y
3y - 4/y - 1 = 0
Умножаем всё на y
3y^2 - y - 4 = 0
(y + 1)(3y - 4) = 0
y1 = -1 ⇒ tg(x/4) = -1 ⇒ x/4 = 3π/4 + πk, k ∈ Z
x1 = 3π + 4πk, k ∈ Z
y2 = 4/3 ⇒ tg(x/4) = 4/3 ⇒ x/4 = arctg(4/3) + πk, k ∈ Z
x2 = 4arctg(4/3) + 4πk, k ∈ Z
Ответ: x1 = 3π + 4πk, k ∈ Z; x2 = 4arctg(4/3) + 4πk, k ∈ Z