sin3x+П/4 =(Меньше или равно)= -корень(2)/2

sin(3x+П/4)≤√2/2

-π-arcsina<x<arcsina+2πn, n∈z

-π-π/4+2πn<3x+П/4<π/4+2πn, n∈z

-2π/2-π/2+2πn<3x<2πn, n∈z

-3π/2+2πn<3x<2πn, n∈z

-π/2+2πn/3<x<2πn/3, n∈z