求函数Y=SIN(π/6-X)的递减区间

2kπ+π/2<=π/6-X<=2kπ+3π/2

2kπ-π/2<=x-π/6<=2kπ+π/2
2kπ-π/3<=x<=2kπ+2π/3
k属于自然数

2kπ+π/2<=π/6-X<=2kπ+3π/2
2kπ-π/2<=x-π/6<=2kπ+π/2
2kπ-π/3<=x<=2kπ+2π/3
k属于整数

先求导，当Y的导数小于等于0的区间就是函数的递减区间。这是最好的解题方法，凡是有关递增递减的连续函数问题基本都能用得上求导。

最好先变一下。y=-sin（x-π/6）求递减区间是
sin（x-π/6）递增区间。
即：2kπ+π/2<=x-π/6<=2kπ+3π/2

左加右减，自己做平移。