y=√2sin(2x+π/4)
最小正周期为 2π/2=π
单调增区间：
2x+π/4∈[2kπ-π/2,2kπ+π/2]
x∈[kπ-3π/8,kπ+π/8]
所以单调增区间为[kπ-3π/8,kπ+π/8] k∈z
加半个周期就是减区间
所以
减区间为
[kπ+π/8,kπ+5π/8] k∈z