f(x)=(√2)sin[x-(π/4)]
2kπ+(π/2)≤x-π/4≤2kπ+(3π/2)
2kπ+(3π/4)≤x≤2kπ+(7π/4)
∴函数递减区间为
[2kπ+(3π/4),2kπ+(7π/4)] k∈Z