2) tqx ≥ -1;
-π/4 ≤ x < <strong> π/2;
πn -π/4 ≤ x < π/2 +πn ;n∈Z<br>x ∈ [ -π/4 +πn ;π/2 +πn] ,n∈ Z
3) 2sinx -1 >0 ;
sinx >1/2 ;
π/6 < x < <strong>π -π/6;
π/6 < x < 5π/6;
π/6 +2πn < x < 5π/6+2πn ,n∈ Z.<br>5) -√3 ≤ 3ctq(2x+π/5) ≤1;
-1/√3 ≤ ctq(2x+π/5) ≤1/3;
arcctq1/3≤ 2x+π/5 ≤ 2π/3 ;
-π/5 +arcctq1/3≤ 2x ≤ 7π/15 ;
-π/5 +arcctq1/3 +πn ≤ 2x ≤ 7π/15+πn;
-π/10 +1/2*arcctq1/3 +π/2*n ≤ x ≤ 7π/30+π/2*n ; n∈Z.