tg²x - 1 = 0
tg²x = 1
tg x = ±1
tg x = 1 или tg x = -1
x₁ = arctg (-1) + πn x₂ = arctg 1 + πn
x₁ = 3π/4 + πn, n∈Z x₂ = π/4 + πn, n∈Z
ответ: x₁ = 3π/4 + πn, n∈Z ; x₂ = π/4 + πn, n∈Z
