1.（2X+π/4）属于（-π/2+2kπ,π/2+2kπ）；k属于Z
得：X属于（-3/8π+kπ,π/8+kπ）,k属于Z
2.X=π/8时,有最大值3；X=π/2时,有最小值3/2倍根号2
3.（-2X+π/4）属于（π/2+2kπ,3π/2+2kπ）；k属于Z
得：X属于（-5π/8+kπ,-π/8+kπ）；k属于Z.注：k与-k等价,k属于Z时.