判别式大于等于0
16cos²θ-24sinθ>=0
2(1-sin²θ)-3sinθ>=0
2sin²θ+3sinθ-2<=0
(sinθ+2)(2sinθ-1)<=0
-2<=sinθ<=1/2
sinθ>=-1
所以-1<=sinθ<=1/2
所以2kπ-7π/6<=θ<=2kπ+π/6
哦,你说得对,应该是3sinθ≠0
θ不等于kπ
所以是
2kπ-7π/6<=θ<2kπ-π,2kπ-π<θ<2kπ,2kπ<θ<=2kπ+π/6