sinθ2kπ-7π/62kπ-π/4最后的答案是怎么合并的？？ 谢谢！对一个确定的k,2kπ-7π/6<2kπ-π/4<θ<2kπ+π/6<2kπ+π/4,且2kπ+π/4-（2kπ-7π/6）=17/12π<2π