-π < -2 < 0
-π < -1 < 0
-2 ≈ -2π/3
-1 ≈ -π/3
на интервале (-π, 0)
-1 <= sin(x) < 0
sin(x) = -1 при х = -π/2
-2 < -π/2 < -1
значит x ∈ (-2, -π/2) U (-π/2, -1)
