因为函数y=sinx在[-π/2+2kπ,π/2+2kπ],所以-π/2+2kπ《-3x+π/4《π/2+2kπ,得-3π/4+2kπ《-3x《π/4+2kπ,解得-π/12-2/3kπ《x《π/4-2/3kπ,因为k属于整数,所以π/12+2/3kπ《x《π/4+2/3kπ是-π/12啊。。。。因为函数y=sinx在[-π/2+2kπ，π/2+2kπ]，所以-π/2+2kπ《-3x+π/4《π/2+2kπ，得-3π/4+2kπ《-3x《π/4+2kπ,解得-π/12-2/3kπ《x《π/4-2/3kπ,因为k属于整数，所以-π/12+2/3kπ《x《π/4+2/3kπ打漏了，对不起