1) cos(3x/4)=0
2) sinx>-1/2
3) ctgx< или = 1

1) cos(3x/4)=0(3x/4)=π/2+πn, n∈Zx=(4/3)(π/2+πn)=2π/3+4πn/3,  n∈Z2) sinx>-1/22πn+π+arcsin(1/2) <x<2πn-arcsin(1/2)2πn+π+π/6 <x<2πn-π/63) ctgx≤ 1(π/4  +πn)  ≤x <(π+πn),n∈Z