对Y求导得y`=2sinx-1,得X=π/6,因为定义域是(-π/2,π/2）,所以,在-π/2到π/6递减,在π/6到π/2递增,π/6为最小值,最大值在-π/2和π/2中产生.
代入得最小值为根号3,最大值为无穷