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

1) cos(3x/4)=0
(3x/4)=π/2+πn, n∈Z
x=(4/3)(π/2+πn)=2π/3+4πn/3,  n∈Z

2) sinx>-1/2

2πn+π+arcsin(1/2) <x<2πn-arcsin(1/2)
2πn+π+π/6 <x<2πn-π/6

3) ctgx≤ 1

(π/4  +πn)  ≤x <(π+πn),n∈Z