The results show that: (1) sin α > 1 / 2; (2) cos α > 1 / 2; (3) Tan α > 1 / 2
(1)sinα>1/2
5 π / 6 + 2n π > α > π / 6 + 2n π (n belongs to Z)
(2)cosα>1/2
π / 3 + 2n π > α > - π / 3 + 2n π (n belongs to Z)
(3)tanα>1/2
(n + 1) π > α > arctan (1 / 2) + n π (n belongs to Z)
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