要y = -sin(2x + π/4)单调递减,
则sin(2x + π/4)单调递增,
∴ -π/2 + 2kπ ≤2x + π/4≤π/2 + 2kπ
∴-3π/4 + 2kπ≤2x≤π/4 + 2kπ,k∈Z
∴-3π/8 + kπ≤x≤π/8 + kπ,k∈Z
∴单调减区间：[-3π/8 + kπ,π/8 + kπ],k∈Z