2cos(П/6-x/2) ≥ tg3П/4 (tg(3П/4)=-1;)
2cos(П/6-x/2)>=-1
cos(П/6-x/2)>-1/2
-2П/3+2Пn<=П/6-x/2<=2П/3+2Пn; n e Z</em>
-2П/3-П/6+2Пn<=-x/2<=2П/3-П/6+2Пn; n e Z </em>
-5П/6+2Пn<=-x/2<=П/2+2Пn; n e Z </em>
5П/6-2Пn>=x/2>=-П/2-2Пn; n e Z
5П/3-4Пn>=x>=-П-4Пn; n e Z