解由y=cos(π/4-x)=cos(x-π/4)
故当2kπ+π≤x-π/4≤2kπ+2π,k属于Z时,y=cos(x-π/4)是增函数
故当2kπ+5π/4≤x≤2kπ+9π/4,k属于Z时,y=cos(x-π/4)是增函数
故y=cos(x-π/4)的增区间为[2kπ+5π/4,2kπ+9π/4],k属于Z.
解由y=cos(π/4-x)=cos(x-π/4)
故当2kπ+π≤x-π/4≤2kπ+2π,k属于Z时,y=cos(x-π/4)是增函数
故当2kπ+5π/4≤x≤2kπ+9π/4,k属于Z时,y=cos(x-π/4)是增函数
故y=cos(x-π/4)的增区间为[2kπ+5π/4,2kπ+9π/4],k属于Z.